Easy 30-Minute Chicken Fajitas

to 3 tablespoons olive oil, or as necessary

to 1.25-pounds boneless skinless chicken breasts, sliced into 1/2-inch strips

medium/large sweet Vidalia onion, thinly sliced

medium red bell pepper, cut into thin strips (orange or green peppers may be substituted)

medium yellow bell pepper, cut into thin strips

water

packet Old El Paso Fajita Seasoning Mix

8-count package Old El Paso Flour Tortilla Shells, for serving

guacamole, sour cream, cheese, lime juice, etc. or your favorite toppings, optional