Cook Manicotti shells. Cook green pepper and onion in 2 Tablespoons butter until tender, set aside. Combine eggs, cottage cheese, 1/4 cup parmesan and crushed marjoram. Add choice of cooked vegetables, tuna, green pepper and onion and mix well. Spoon into cooked manicotti shells. Arrange stuffed shells in a single layer in a 12 x 7.5 x 2 dish.
In saucepan melt 3 Tablespoons of butter. Blend in flour, salt and pepper. Add milk all at once. Cook and stir til thickened and bubbly. Add shredded cheese, stirring to melt; pour over stuffed shells. Sprinkle with 1/4 cup parmesan. Cover and bake in 350 oven 35 to 40 minutes or until heated through.