Penne Casserole with Ground Beef and Mushroom

My variation of Ziti Casserole with Ground Beef and Mushrooms from:
http://southernfood.about.com/od/hamburgcasseroles/r/r100130b.htm

Ingredients:

• 8 oz or 225g Penne pasta
• 1/2 tbsp olive oil
• 1/2 lb ground beef
• 1/2 cup onion, diced
• 1/2 bell pepper, chopped
• 2 to 3 oz or 85g mushrooms, sliced
• 12 oz spaghetti sauce ( I used only 7 oz )
• 1/2 can (5 1/4 oz) cream of mushroom soup (To prepare Cream of Mushroom Soup, see link:  http://www.blogger.com/blogger.g?blogID=6416683131238773679#editor/target=post;postID=8976703585321092263)
• 7 oz or 200g tomatoes, diced
• salt and pepper to taste
• 2 cups shredded mozarella cheese ( I used only 1 cup)

Preparation:

1. Cook pasta according to package directions to al dente consistency.
2. Heat oil in a large skillet over medium heat and brown the ground beef about 5 minute.
3. Add onion, green bell pepper and mushrooms and continue cooking, stirring, until beef is no longer pink and vegetables are tender.
4. Stir in spaghetti sauce, cream of mushroom soup and diced tomatoes.
5. Allow to boil and simmer 5 minutes, add salt and pepper to taste.
6. Grease a baking dish with butter. Spread half of the pasta, spoon half of the sauce over the pasta, then top with half of cheese. Repeat layers with the remaining pasta, sauce and cheese.
7. Bake for 20 to 30 minutes at 175 deg F, until hot and bubbly.