Preheat oven to 400. Place the shredded chicken and spaghetti squash in a greased 9x13 casserole dish.
Heat the butter and olive oil in a large skillet over medium heat until hot.
Add the onions and garlic and cook until softened. Next, add the mushrooms and cook until tender.
Add the vegetables to the casserole.
Combine the sauce ingredients and mix until smooth.
Pour the sauce over the filling in the casserole dish. Mix it into the chicken and squash.
Top with the cheese.
Bake for 20-25 minutes or until hot and bubbly.
Notes
How to Cook Spaghetti SquashInstant Pot - Add one cup of water and a rack to the pressure cooker. Cook a 3 lb halved and seeded squash on high pressure for 5 minutes. Quick release.Oven - Cook a 3 lb halved and seeded squash, cut side down, for 40-50 minutes at 400. It is done when it is fork-tender.Air Fryer - Cook a 3 lb quartered and seeded squash for 15-20 minutes at 400. It is done when it is fork-tender.