Wash squash; pierce and cook in oven at 350° for about one hour or until tender. If using the microwave, pierce squash and cook for approximately 10 minutes or until squash is tender. Cool. Cut squash in half and remove seeds. Using a fork, remove spaghetti-like strands. Measure 4 cups and set aside.
Brown ground beef in a large skillet; drain. Add sauce and simmer, uncovered, for 30 minutes or until thickened, stirring occasionally.
Combine ricotta cheese, eggs, salt, pepper, and Parmesan cheese; mix well. In a 9-x-13-inch baking dish, layer half of the spaghetti squash, half of the cheese mixture, half of the meat sauce, and half of the mozzarella cheese. Repeat layers. Bake at 375° for 30 minutes. Allow it to stand for 10 minutes before serving.