To a small bowl, mix all the fajita seasoning ingredients.
Heat the oil in a large skillet over medium-high heat. Add the garlic together with the onion and saute for 2-3 minutes. Add the peppers, then sprinkle with ½ of the fajita mix and cook for 3 minutes more. Set aside.
Cut a lengthways pocket to each chicken breast. Rub the chicken with the remaining fajita seasoning all over, then stuff the pocket with a spoonful of fajita-pepper mixture and cheddar cheese. Seal with a toothpick by inserting it diagonally, to keep the stuffing in.
To the same skillet, add the remaining oil and sear the chicken breast for 4-5 minutes per side.
Next, add ¼ cup of water to the pan, cover, and cook over low heat for 6-8 minutes, or until the chicken is fully cooked through.
Garnish with fresh parsley and serve with lime wedges if desired.
