1. For salsa, in a bowl combine tomato, green sweet pepper, onion, jalapeno peppers, garlic, cilantro, and salt. Set aside 2 tablespoons of the salsa. Cover and chill remaining salsa until serving time.
2. In another bowl combine ground beef and the 2 tablespoons of salsa; mix well. Shape mixture into six 1/2-inch-thick oval patties. Grill patties on an uncovered grill directly over medium coals for 13 to 15 minutes or until an instant-read thermometer inserted in side of patty registers 160 degrees F., turning patties once halfway through grilling time. Arrange shredded lettuce on individual plates. Top with burgers, remaining salsa, and cheddar cheese. Serve with sour cream and/or guacamole.
To grill by indirect heat: Arrange preheated coals around a drip pan in a covered grill. Test for medium heat above pan. Place patties on grill over drip pan. Cover and grill for 18 to 20 minutes or until no pink remains, turning patties once halfway through grilling time.
Make-ahead tip: Prepare salsa; cover and chill up to 24 hours. Use 2 tablespoons salsa for burgers. Serve burgers with remaining salsa.