Preheat oven to 350 degrees F.
Melt half of the butter in a large skillet over medium heat. Add onion and saute until soft. In a separate skillet, saute the squash in the remaining butter until soft. Alternatively, you can cook the squash in the microwave. Drain excess liquid from squash.
Butter a casserole dish and then combine the onion, squash, cheese, green chiles, and soup in the casserole dish. Bake until heated through and cheese is well melted. Remove from oven, stir, and sprinkle bread crumbs on top. Return to the oven and bake 5 more minutes, or until bread crumb mixture is golden.