Remove and discard stems from mushrooms. Place mushrooms, cap side up, on a baking sheet coated with non-stick cooking spray. Brush tops with oil.
Broil 4-6 inches from the heat for 4-5 minutes or until tender.
Spread half of the spaghetti sauce into an 11 inch by 7 inch by 2 inch baking dish coated with nonstick cooking spray. Place mushrooms on sauce, cap side down. Sprinkle with fontina cheese. Drizzle with remaining spaghetti sauce. Sprinkle with parmesan cheese.
Bake uncovered at 350 degrees for 8-10 minutes or until heated through.