Chicken and Mushroom Casserole

• 4 -5 large boneless chicken breasts (, trimmed and cut into 1 -inch thick strips)
• Salt and Pepper to taste
• 1 cup all-purpose flour to coat the chicken
• 6 Tbsp olive oil (, divided)
• 1 pound fresh mushrooms (, thickly sliced)
• 1 medium onion (, finely diced)

Ingredients for the Sauce:

• 3 Tbsp unsalted butter
• 3 Tbsp all-purpose flour for the sauce
• 1 1/2 cups chicken broth
• 1 Tbsp lemon juice
• 1 cup half and half ((or 1/2 cup milk + 1/2 cup heavy cream))