Place the chicken, peppers, and onions in a mixing bowl, and mix in the olive oil and fajita spice mix.
4 Chicken Breasts, 2 Peppers, 1 Onion, 1 tablespoon Olive Oil, 2 teaspoon Cumin, 2 teaspoon Smoked Paprika, 2 teaspoon Oregano, 1 teaspoon Chilli Powder, 1 teaspoon Garlic Powder, ¼ teaspoon Cayenne, ½ teaspoon Salt, ¼ teaspoon Pepper