Chicken Pizzarella

Yield:	8 Servings
Categories:	Poultry

1	tb	Olive oil
2	tb	Onion; finely chopped
1	c	Mushrooms; thickly sliced
1		Clove (small) garlic; minced
1/2	ts	Oregano
1	cn	(8-oz) tomato sauce
		Pepper to taste
8		Chicken breast halves; boneless
1	c	Sliced Mozzarella cheese