In a large saucepan, saute onion and green pepper in olive oil until tender. Add garlic; cook 1 minute longer. Stir in all remaining sauce ingredients; bring to a boil. Reduce heat; cover and simmer for 1 hour, stirring occasionally. Uncover, simmer 10-15 minutes longer or until thickened.
Meanwhile, for manicotti, cook beef and onion in a skillet until the meat is no longer pink. Add garlic; cook 1 minute longer. Drain; cool slightly.
Squeeze spinach thoroughly to remove excess water; add to the skillet with 1/2 cup Parmesan cheese, eggs, oregano, salt and pepper. Mix well. Refrigerate 1-1/2 cups of the sauce (makes 4 cups)
For another recipe.
Pour 1 cup of the remaining sauce into a 13-in. x 9-in. baking dish. Stuff manicotti with the meat mixture; arrange over the sauce. Pour another 1-1/2 cups of sauce on top. Sprinkle with the mozzarella and remaining Parmesan cheese.
Bake, uncovered, at 350° for 25-30 minutes or until a thermometer reads 160°. Yield: 7 servings.