PREHEAT oven to 350° F.
COMBINE ricotta cheese, pesto, 3/4 cup mozzarella cheese, Parmesan cheese and eggs in large bowl; stir well. Pour about 1 cup marinara sauce over bottom of 13 x 9-inch casserole dish. Spoon about 2 tablespoons ricotta filling into each cooked shell. Place filled shells, side by side, into casserole dish. (At this point, the dish can be made and refrigerated for up to 24 hours.) Spoon the remaining marinara sauce over the stuffed shells. Sprinkle with remaining 1/4 cup mozzarella cheese; cover.
BAKE for 35 minutes or until bubbly and cheese is melted (if using refrigerated shells, bake for about 45 minutes).