Preheat oven to 350 degrees F (175 degrees C).

Bring a large pot of salted water to a boil. Add squash and onion and cook until tender but still firm, about 15 minutes. Drain and transfer to a 2 quart casserole dish.

In a medium bowl combine soup, cheese and eggs. Mix well and pour into dish with squash.

Bake in preheated oven for 25 minutes. Remove from oven and sprinkle croutons on top. Return to oven and bake for 20 minutes more.