Warm the butter with the olive oil in a nonstick frying pan over medium heat.
Stir in the diced onion and cook for about 2 minutes.
Stir in the cooked chicken pieces and season with salt and pepper to taste, onion powder, garlic powder, chili powder, dried oregano, and yellow mustard.
Stir in the cream of chicken powder soup and pour in the pasta water and whole milk.
Add the cooked pasta and stir until everything is combined and thickened.
It will take about 3-4 minutes.
Transfer the whole mixture to a casserole pan well brushed with olive oil and cover the whole surface with grated cheese.
Bake in an already heated oven at 350F or 180 C degrees for about 15-20 minutes