Preheat oven to 350 degrees F (175 degrees C). Lightly grease an 8x8-inch baking dish.
Arrange zucchini slices in the bottom of the baking dish; spread with mushroom soup. Top with fontina cheese and sprinkle with fried onions.
Bake in preheated oven until mushroom soup is bubbly and cheese is melted, about 30 minutes.
I like this dish just the way it is, but you can make it zestier with the addition of spices of your liking directly to the zucchini before adding the other ingredients. This is also good with other concentrated soups, including cream of mushroom and cream of celery. Make it healthier by using low fat cheeses and soup.