- 2 (1 ounce) packages dry onion soup mix
- 1 (16 ounce) package thin spaghetti, broken into halves
- 1 tablespoon butter, or to taste
- 1 cup chopped green bell pepper
- 2/3 cup coarsely chopped onion
- 3 cups quartered zucchini slices
- 1 (28 ounce) can petite diced tomatoes
- 1/4 cup parsley
- 1 teaspoon salt
- 1/8 teaspoon ground black pepper
- 1 1/4 cups shredded Swiss cheese
- 1 1/4 cups shredded mozzarella cheese
- Preheat oven to 350 degrees F (175 degrees C).
- Bring a large pot of water to a boil. Stir onion soup mix into the boiling water. Cook spaghetti in the boiling water, stirring occasionally, until barely tender, 6 to 7 minutes; drain. Pour spaghetti into a casserole dish.
- Melt butter in a large skillet over medium heat. Cook and stir bell pepper and onion in hot butter until slightly tender, about 4 minutes; add zucchini, place a cover on the skillet, reduce heat to medium-high, and cook until zucchini is soft, about 10 minutes.
- Stir tomatoes, parsley, salt, and pepper into the vegetable mixture; replace cover and cook until the tomatoes are heated through, 3 to 5 minutes.
- Pour the vegetable mixture over the spaghetti and mix. Spread Swiss cheese and mozzarella cheese over the vegetable and pasta mixture. Cover dish with aluminum foil.
- Bake in preheated oven until heated in the center, about 40 minutes.