baked spaghetti casserole

Ingredients

• 1 cup onion, chopped
• 1 cup green pepper, chopped
• 1 tablespoon butter or margarine (i used nonstick cooking spray)
• 2 (14 oz.) cans diced tomatoes, undrained
• 1 (4 oz.) can mushroom stems and pieces, drained
• 1 can (2.25 oz.) sliced ripe olives, drained
• 2 teaspoons dried oregano
• 1 pound ground beef, browned and drained* (see my notes)
• 12 ounces spaghetti, cooked and drained according to package directions
• 2 cups (8 oz.) shredded cheddar cheese
• 1 can (10.25 oz.) condensed cream of mushroom soup
• 1/4 cup water
• 1/4 cup grated parmesan cheese