Instructions

1. Preheat the oven to 400 degrees.
2. Melt the butter in a large skillet over medium-low heat.
3. Add the onions, stirring into the butter and cook until the onions have completely softened, about 10 minutes.
4. Stir in the garlic and cook one minute longer.
5. Add the mushrooms, salt, pepper, poultry seasoning and rosemary then cook until the mushrooms are browned, about 5 minutes.
6. Stir in the frozen peas and carrots then add the flour and stir to combine. Cook for a minute while stirring, then slowly pour in the milk.
7. Using a wooden spoon, scrape up the bottom of the skillet and stir the milk into the vegetables. Let the filling come up to a simmer and then let thicken for 3-4 minutes.
8. Stir in the chicken and 1/4 cup of the parmesan cheese, then remove the skillet form the heat. Taste for seasonings and adjust if needed.
9. Pour the filling into a large bowl along with the cooked spaghetti squash. Stir gently to combine the filling, then pour into a 9″ x 13″ baking dish that’s been buttered or sprayed with cooking spray.
10. Top the casserole with the remaining parmesan cheese and breadcrumbs then bake for 30 minutes.
11. To brown the topping even more, place the casserole under the broiler for 3-4 minutes.