Place the flattened chicken thighs in a bowl (ask your butcher to flatten them for breading).

Spread mustard, black pepper, and garlic salt on both sides of the chicken thighs. Let marinate for 20 minutes.

In a saucepan, add a splash of oil and the sliced quarter onion. Cook until the onion is translucent, about 3 minutes.

Add the chicken thighs and cook for 5 to 10 minutes on each side until golden brown.

Serve with some white rice and cooked nopales (cactus paddles).