Season the chicken with onion powder, salt, and pepper.
In a pan over medium heat, cook for 8 minutes per side or until golden.
Transfer to cutting board and cut into strips. Set aside
For the Sauce
Place a saucepan over medium heat, add the butter and milk and stir occasionally until butter is melted. Add parmesan and mozzarella cheese and whisk gently until cheese is melted and combined.
Once the butter is melted, add the black pepper and garlic.
Stir until well mixed and simmer for 5 minutes. Set aside.
For the Pasta
In a medium sized pot bring water to a boil, place the spaghetti and cook following the package instructions, about 7 minutes.