Instructions: 1. Form beef into 20 three-inch diameter patties. Form cheese into 10 1 1/2-inch rounds; place cheese rounds atop 10 beef patties. Top each with another beef patty, sealing at edges. Season with pepper. (Can be prepared one day ahead. Place between layers of waxed paper. Cover and chill.)

2. Prepare barbecue (medium-high heat) or preheat broiler. Brush barbecue rack with vegetable oil. Grill burgers until charred outside but still juicy, about three minutes per side.

3. Grill bread slices until lightly toasted, about 1 minute per side. Place each burger on one bread slice. Top with tomato, onion, arugula and another bread slice and serve.

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