Baked White Spaghetti

Ingredients

• 1 cup chopped onion
• 1 cup chopped green pepper
• 1 Tablespoon butter
• 1 can (28 ounces) diced tomatoes, undrained
• 1 can (4 ounces) mushroom stems and pieces, drained
• 2 teaspoons dried oregano
• 1 pound ground beef, browned and drained, optional
• 12 ounces spaghetti, cooked and drained
• 2 cups (8 ounces) shredded cheddar cheese
• 1 can (10-3/4 ounces) condensed cream of mushroom soup
• 1/4 cup water
• 1/4 cup grated Parmesan cheese