Thaw corn soufflé according to package directions, and set aside.
Melt butter in a skillet over medium-high heat; add onion, and sauté 5 minutes or until tender. Add squash, and sauté 5 minutes.
Stir together corn soufflé, squash mixture, cheese, and next 5 ingredients. Spoon mixture into a lightly greased 8-inch square baking dish.
Bake at 350° for 50 minutes or until set. Let stand 10 minutes before serving.