Pat the skirt steak dry with paper towels and remove any extra fat.
Prepare a fajita marinade by combining lime juice, olive oil, orange juice, garlic, chili powder, black pepper, cumin, coriander, salt and cilantro in a blender and blend until smooth. Remove ¼ cup of the marinade and pour the rest in a resealable plastic bag or shallow dish. Add the skirt steak to the marinade, ensuring it's fully coated, and let it marinate for at least 2 hours in the refrigerator.
Preheat a grill to medium-high heat.
Cook the steak 2-3 minutes per side, to an internal temperature of about 130°F for medium-rare, depending on the thickness of the steak. For the best results, hotter is better. Aim for a quick sear to lock in the juices while maintaining the tender interior. Don’t overcook it.
After cooking, transfer the steak to a cutting board and let it rest for about 5 minutes. Resting allows the juices to redistribute throughout the meat, ensuring juicy and flavorful fajitas.
While the steak is resting, cook the onions, red bell pepper and poblano pepper on a hot griddle or skillet with a little vegetable oil for about 6 minutes.
Once rested, slice the steak across the grain into thin strips, about ¼” wide. Cutting across the grain shortens the muscle fibers, resulting in more tender meat. Finish the steak strips on the hot griddle or skillet alongside the vegetables for 2 additional minutes.
Warm the tortillas on the griddle or in a skillet for 5-10 seconds on each side. Then, fill each warm tortilla with a generous portion of sliced steak, along with sautéed onions, red bell peppers and poblano peppers.
Top with a drizzle of the reserved marinade and your favorite garnishes, such as Pico de Gallo, Mexican Crema or sour cream, and fresh cilantro. Serve with Mexican rice and black or refried beans for a satisfying meal.