In a small bowl, combine the garlic powder, onion powder, paprika, Italian seasoning, Old Bay seasoning, salt, and cayenne (if using) and mix until even.
Lay the chicken tenderloins flat on a tray or plate and sprinkle the seasoning over one side; lightly pat to adhere. Turn the tenders and sprinkle the remaining seasoning on the other side, patting again. Refrigerate up to 1 hour if desired.
Heat a large cast iron skillet over high heat for 2–3 minutes, then reduce heat to medium-high and add the butter.
Once the butter has melted and begins to brown but not smoke, arrange the seasoned chicken in a single layer in the skillet without crowding; cook in batches if needed.
Cook the tenders undisturbed for 2–3 minutes on the first side, flip and cook 2 minutes on the other side.
Reduce the heat to low, cover the pan, and continue cooking until the internal temperature reaches 165°F (about 1–2 more minutes).
Remove the chicken from the skillet to stop further cooking and serve warm. Garnish with fresh parsley or a squeeze of lemon if desired.
