Cook pasta. Drain immediately. Rinse with cold water; drain well.
Meanwhile, drain thawed spinach well, pressing out excess liquid.
For filling, combine eggs; ricotta, mozzarella, and cheddar cheese; half of the Parmesan cheese; and the spinach. Spoon about 3 tablespoons filling into each jumbo shell or about 1/3 cup filling into each manicotti shell.
Place 4 jumbo shells or 2 manicotti shells into each of 4 individual casseroles. Top with sauce; sprinkle with remaining Parmesan cheese. Bake 2 casseroles immediately; freeze remaining casseroles as directed.
Makes 4 servings. To Eat Two: Bake 2 of the casseroles, covered, in a 350 degree F oven about 25 minutes or until heated through.
To Freeze Two: Seal, label, and freeze 2 of the casseroles for up to 3 months. To serve, bake 1 or 2 of the frozen casseroles, covered, in a 375 degree F oven about 1 hour or until heated through.