1) Preheat the oven to 180C/Gas 4. Grease a 2L casserole dish.
2) Heat the oil in a large skillet over medium heat. Saute the squash, onion and butter until soft. Transfer to a bowl and stir in the Parmesan, Cheddar and sour cream. Add salt and pepper, to taste.
3) Place the squash mixture in the prepared casserole dish and sprinkle the cheese biscuit crumbs evenly over the top. Bake for 20 minutes or until the top is golden and bubbly.