Preheat oven to 350 degrees F. Butter a 9 x 13-inch dish.
For topping, combine all ingredients and set aside.
For filling, heat oil in a saute pan, add onions and cook for 3 to 4 minutes or until they are soft. Add yellow squash and saute for 3 to 4 minutes. Transfer to large bowl and add remaining ingredients and toss gently. Place mixture into prepared pan. Cover with topping and bake 30 to 35 minutes or until thoroughly heated. Serve.