Preheat oven to 350 degrees F.
Slice ends off washed squash and zucchini, and then slice each in half lengthwise. Then cut into bite-sized pieces. Chop onion.
Mix all ingredients together and spread in your choice of casserole dish.
Bake uncovered for 30-40 minutes, or until squash is cooked and cheese mixture has melted and started to brown.
Cool briefly and serve.