Michele's Polenta with sausage and peppers

4 T olive oil
1/2 stick butter
4 tsp crushed garlic
3 medium onions quartered
3 green peppers any color quartered
2 cans mushroom buttons, or fresh if you have them 1 pound fresh sliced
1/2 cup parmesan cheese
3 lbs sausage cut in 1 inch pieces
salt and pepper to taste
1 T oregano
1 T garlic salt
1 30 oz can whole tomatoes squeezzed to break them up