1. Heat broiler. Lightly coat broiler-pan rack with nonstick cooking spray.
2. Saute onion and mushrooms in oil in large nonstick skillet until softened, 8 minutes. Add soy sauce; cook 2 minutes. Remove to small bowl.
3. Whirl rice, onion mixture, parsley and fontina in food processor until finely chopped. Combine with bread crumbs, egg, tomato, salt if using and pepper in large bowl. Using wet hands, shape into 6 equal patties. (Can be made 24 hours ahead; cover; refrigerate. Remove from refrigerator 20 minutes before broiling.)
4. Broil burgers 6 inches from heat for 4 minutes per side, until cooked through and crusty on outside. Place burgers in rolls and top with salsa.
1. Combine tomato, onion, parsley, and vinegar in a bowl