In a small bowl, combine the chili powder, cumin, oregano. Sprinkle both sides of the chicken with salt, pepper and the spice mix.

Heat 1 Tbs. of the oil in a medium skillet over medium-high heat. Add the chicken and cook until just cooked through, 2 to 3 minutes per side. Transfer the chicken to a cutting board, let rest 5 minutes, then cut into cubes. Set aside.

Add the remaining 1 Tbs. oil to the skillet over medium-high heat. Add the onions and peppers and cook, stirring often, until softened, 3 to 4 minutes. Remove and set aside.

Melt 1 Tbs. of the butter in a separate skillet or griddle over medium heat. Place a flour tortilla in the skillet, top with grated cheese, some of the chicken pieces and cooked pepper mixture. Top with a little more grated cheese and top with a second tortilla.

When the tortilla is golden on the first side, carefully flip the quesadilla to the other side, adding another ½ tablespoon butter to the skillet at the same time. Continue cooking until the second side is golden. Repeat with the remaining tortillas and fillings.

Cut each quesadilla into wedges and serve with salsa, guacamole, and sour cream if desired.