Chicken Tetrazzini Casserole

Ingredients:
5 tbsp Branch and Vine Garlic Olive Oil
1 1/2 lbs. Boneless, Skinless Chicken thighs, cut into 1-inch pieces
Kosher Salt and Ground Black Pepper, to taste
6 tbsp Butter
2 Ribs of Celery
1 lb. Mushrooms, thinly sliced
1 Yellow Onion, chopped
1 Red Bell Pepper, chopped
1/2 cup White Wine
1/4 cup All-Purpose Flour
1 cup Chicken Broth
1 cup Whole Milk
6 oz Cheddar Cheese
1/2 cup Grated Parmesan Cheese
1 lb. Spaghetti
3/4 cup Frozen Peas