Break spaghetti into 2-inch pieces and cook according to package directions; drain. In a large bowl, beat eggs. Gradually add milk, 1 cup mozzarella cheese, spinach and garlic powder. Stir in spaghetti pieces. Lightly oil a 10 1/2 x 15 1/2 x 1 1/2-inch baking pan. Spread spaghetti mixture into pan, building up sides slightly. Bake at 425° F for 15 minutes. Remove from oven.
Spread spaghetti sauce over spaghetti "crust." Spread broccoli and zucchini over sauce and sprinkle with remaining mozzarella cheese. Bake at 350° F for 35 minutes. Let stand 5 minutes before cutting.