Combine flour, garlic powder, onion powder, paprika, salt and cayenne pepper in a shallow bowl.
Heat oil over medium heat in a large nonstick pan. Dredge the chicken in the flour mixture on both sides. Reserve the flour mixture for later in the process.
Place chicken into the pan and cook, about 10-12 minutes per side, until golden brown and cooked through. (If the pan looks dry, add a little more oil.) Remove the chicken onto a separate plate.
To the pan, add butter, garlic, onions, celery and peppers. Saute until the vegetables are soft and sizzling.
Stir in the reserved flour mixture and cook 1-2 more minutes.
Pour in the chicken stock. Raise the heat to a boil, then reduce to a simmer. Place the chicken back into the pan and simmer until thickened. Serve warm.