Heat olive oil in a large skillet over medium-high heat. Add the sliced chicken breast to the skillet and season with salt, pepper, chili powder, and cumin. Cook for about 5-7 minutes, stirring occasionally, until the chicken is cooked through and no longer pink.
Once the chicken is cooked, add the sliced bell peppers and onion to the skillet. Sauté the vegetables with the chicken for an additional 5-7 minutes, until the peppers and onions are tender.
Remove the skillet from heat and sprinkle the crumbled feta cheese over the top of the chicken and vegetables. Allow it to melt slightly before serving.
Garnish with fresh cilantro, if desired, and serve hot. Enjoy your Chicken Fajita Skillet with tortillas or on its own!