Instructions: MEXICAN food has gotten a bad rap as fattening and filling. Maybe thats because the burritos and beans hog the spotlight while their lighter, more nutritious cousin, the nopal cactus, sulks offstage in the dark.

In what has become a vicious cycle of neglect, the nopal is absent from most Mexican restaurant menus, so consumers dont know much about it and therefore major supermarket chains dont carry it. No wonder that many non-Mexicans overlook this vegetable with its delightful tart green-bean taste.

But just because nopales are hard to find doesnt mean they should be banished as edible outcasts. In fact, there are many culinary, cultural and medicinal reasons to invite nopales - the leaves of the prickly pear cactus - to your dinner table.

``Many people dont know it, but nopales are very important in the Mexican diet, says Franciso Cisneros, chef at Guaymas Restaurant in Tiburon.

``Its really the national vegetable.

Nopales are believed to come from Mexico because the country is teeming with the plants. Many a Mexican highway is hemmed in by thousands of the plants, standing firm in the face of gusty winds sweeping through swaths of undeveloped land.

The image of the nopal can be found on ancient paintings and books.

Shamans or sorcerers consider the nopal to be a talisman capable of warding off evil spirits. Even the Mexican flag is graced with the image of the humble nopal.

Visit San Joses Peralta Adobe and Fallon House, 175 W. St. John St., to learn even more about nopales. Tour guides explain how the cactus, which grows densely on the grounds, is best blanched to eliminate most of the sliminess. But ages ago, pioneers often opted for the quick trail-cooking method, where the nopales would be thrown on an open fire until the spines burned off. Then, the outer layer was peeled away and the sticky insides eaten.

Volunteers there demonstrate this cooking method every Founders Day in November, as well as other times throughout the year for special events.

Other folks need a nopales-fix much more frequently. Mexican immigrant Pepe Rojas loves nopales so much that he grows them outside his Fair Oaks apartment. He loves their taste, and they remind him of home. Sometimes his wife prepares them in the traditional way that reduces the gooey liquid inside them. Other times, he just picks off the thorns and throws the raw vegetables, including their juice, on the grill.

``I cant live without them, says Rojas. ``Theyre something I really love, and they are very nutritious.

Nopales are cholesterol-free, low in sodium, and high in fiber and vitamin C. Beauty companies have made sun and wrinkle protection products with the nopal because of its high content of vitamin A.

Mexican government studies show that eating nopales can help control diabetes, a disease caused by deficiency of the insulin that helps body tissues use blood sugar. Nopales, researchers believe, trigger sugar processing.

Surprisingly, nopales have gained limited popularity outside Mexico, the American Southwest, Japan and Spain. In the Bay Area, they can be found in most Mexican markets, often chopped up and bagged in pound plastic sacks that sell for about $1.50.

If you decide to buy them, youll need to do some groundwork before mixing the nopales with other foods. If you dont find them in these neat bundles and you buy the cactus as paddles, make sure all the thorns have been removed. A vegetable peeler shaves them off nicely. Trim the outside edges of the pads as well, then use a sharp knife to dice the nopales into tiny squares, about the size of confetti pieces.

Resist your temptation to eat them raw; they dont taste like much before theyre cooked.

Rinse the bits and toss them into a gallon of water with a garlic clove and a pinch of salt. Bring the mixture to a boil. Simmer for about 15 minutes. The bright green nopales should fade to olive, and the little pieces should become more supple.

Use a colander to remove the liquid, which includes the water used in cooking, as well as the juice of the nopal. If the nopales do not lose this juice, they become quite sticky, and preparing a nopal dish can be like playing with melted bubble gum.

Once you strain off all the liquid, youre ready to begin to prepare a nopal dish. For an easy side dish, put 3 tablespoons oil in a saucepan and add the nopales, 2 diced tomatoes, 1 small onion diced and serrano chiles to taste. Cook on a low to medium flame for about 20 minutes.

This is the most typical way to make nopales. They can be served warm as a side to a Mexican main dish such as fajitas, or teamed up with mesquite-roasted chicken. If you have leftovers, dont bother to reheat - theyre great for nibbling cold.

Here are some other ways to serve nopales cold after theyve been cooked.

Place heated or cold nopales in a shallow dish and decorate with slices of avocado. Or, if you want to be more elaborate (or if you want to celebrate a Mexican holiday), place the nopales in the center of an oval platter and place on each side fine strips of Mexican cheese known as queso fresco

(look for brands El Mexicano, Cacique and Azteca in most supermarkets).

Then line with slices of tomato to mimic the green, white and red Mexican flag.

Another simple dish is eggs with nopales, which became a revered dish several years ago because it was a favorite of former Mexican President Carlos Salinas de Gortari. When he left office, Salinas was quite unpopular with his electorate, but some voters still eat the dish with gusto. Beat 3 eggs, then pour them into a buttered saucepan. When the eggs begin to jell, throw 1 cup of the cooked mixture of nopales, tomato, onion and chile into the saucepan. Stir frequently until the eggs are cooked.

Serve.

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