Favorite Chicken Tetrazzini

4 tablespoons margarine
2 onions, chopped
1 medium bell pepper, chopped
1 (16 ounce) can tomatoes
4 tablespoons chili powder
Salt, to taste
Pepper, to taste
3/4 cup sharp cheese, shredded
1 pint light cream
Pinch of baking soda
1 (4 to 6 pound) chicken
16 ounces thin spaghetti, cooked

Saut