In a small bowl, combine the fajita marinade ingredients: oil, lemon juice, garlic, cumin, garlic powder, onion powder, salt, and freshly ground black pepper. Mix until well combined.
Next, place the chopped chicken into a large ziplock bag. Pour half of the marinade over the chicken and seal the bag. Massage it gently to coat the chicken, then refrigerate for about 15 minutes.
In another large ziplock bag, toss the chopped onion, green bell pepper, and red bell pepper with the remaining marinade. Seal and shake to coat.
After marinating, heat a large skillet over medium-high heat. Add olive oil to the pan. Carefully add the marinated chicken (discard any remaining marinade) and cook for 3-4 minutes on one side until golden brown.
Flip the chicken and continue cooking until the internal temperature reaches about 165 degrees F. Remove the chicken from the skillet and cover it with aluminum foil to keep warm.
Add the marinated vegetables and the additional minced garlic to the skillet. Sauté for a few minutes until they become tender.
In the same skillet, add the chicken broth, milk, canned tomatoes, uncooked penne pasta, and salt. Stir to combine.
Bring the mixture to a boil over high heat, then cover the skillet and reduce the heat to medium-low. Cook for 13-15 minutes, or until the pasta is tender.
Once cooked, add the sautéed chicken and vegetables back into the skillet. Stir everything together until well mixed.
Serve immediately with optional toppings of salsa and sour cream.
