Mix the meat, bread crumbs, onion, egg and seasonings together.
Shape the mixture into 12 thin patties, each about 4-inches in diameter.
Top each of 6 patties with 1 tablespoon of the cottage cheese, spreading to within 1/2-inch of the edge, sprinkle on 2 teaspoons of the Parmesan cheese, and top each patty with one of the remaining patties sealing the edges firmly.
Brown the patties in a large skillet over medium-high heat, turning once.
Drain off the fat and pour the tomato sauce over the patties.
Cover and simmer for about 15 minutes.
Place a cheese slice on each patty, cover, and heat until the cheese is melted, about 2 minutes.
Serve with the remaining sauce in the skillet poured over them.