Saute the onion in half the butter in a large skillet over medium heat until soft. In another skillet, saute the squash in the rest of the butter until soft (or microwave it). Drain the squash.
Combine the onion, squash, cheese, chiles and soup in a buttered casserole and bake until heated through and the cheese is melted.
Stir, sprinkle with the bread crumbs and bake 5 minutes more, until golden.