Combine the ingredients for the marinade in a large shallow bowl or zip-top bag. Give it a taste to check for seasonings and adjust to preference. Coat the steak with the marinade and let sit covered in the refrigerator for at least 2-4 hours and ideally overnight.
Remove from the refrigerator 30 minutes prior to grilling.
Set a large cast iron skillet or grill pan over high heat and let heat up for a couple of minutes. Add the steak to the pan and fry on each side for about 3-5 minutes or longer if you'd like it more done. Remove the steak from the pan and allow it to rest for several minutes, tented with a piece of foil.
Add the remaining tablespoon of oil to the pan over high heat, and add in the onions, poblano, and bell peppers. Cook for a total of 2-3 minutes or longer if you prefer them softer, season with a pinch of salt and pepper.
Slice the meat against the grain into thin slices. Add it back to the veggies if you'd like.
Serve fajitas in tortillas or on rice bowls topped with your favorite toppings.
