To make the marinade, mix the garlic, chili powder, cumin, coriander, smoked paprika, olive oil, lime juice, orange juice, orange zest, cilantro, salt, and black pepper in a large bowl.
Add the skirt steak to the marinade and turn it over to coat it in the marinade. Cover the skirt steak tightly with plastic wrap and chill it in the fridge for at least an hour.
To cook the skirt steak, place the olive oil into a large grill pan or skillet and place it over a medium-high flame.
Place the skirt steak into the pan and sear it on each side for 3-5 minutes until it has a rich brown crust.
Remove the skirt steak from the stove and place it on a cutting board. Let the skirt steak rest for 5 minutes.
Meanwhile, to cook the vegetables, add the vegetable oil to the same skillet or grill pan and heat it over medium-high heat.
Next add the sliced bell peppers and onions and cook them for 5-10 minutes until they reach your desired level of doneness.
Cut the skirt steak into thin slices across the grain.
Return the skirt steak to the pan with the onions and peppers and cook it for 30 seconds until it is heated.
Remove the steak fajitas from the stove and serve on flour or corn tortillas along with sour cream, guacamole, pico de gallo, lime wedges, or your favorite fajita toppings.
Serve and enjoy!