In a bowl mash beans with a fork; add the rice onion egg and 2 tablespoons salsa; mix well
Season if needed with salt and pepper
Drop by 1/2 cupfuls into a large nonstick skillet coated with cooking spray
Flatten to 1/2-inch thickness; cook over medium heat for 4-5 minutes on each side or until firm and browned
In a small bowl combine sour cream and remaining salsa; on bottom bun place a lettuce leaf burger sour cream mixture and slice of cheese; cover with top bun