Pat the flank steak dry with paper towels and season both sides evenly with chili powder, cumin, garlic powder, sea salt, and black pepper.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until the oil is shimmering.
Sear the steak for 3 to 4 minutes per side until a deep golden crust forms, then transfer to a cutting board to rest for 5 minutes before slicing into thin strips.
In the same skillet, sauté the thinly sliced red bell peppers and red onions for 3 minutes until they are tender-crisp and slightly charred.
Return the sliced steak to the skillet, drizzle with the fresh lime juice, and toss everything together to combine the flavors.
Place the whole wheat tortilla in a clean skillet over medium heat, then layer half of the shredded pepper jack cheese, the steak and pepper mixture, and the remaining cheese on one half of the tortilla.
Fold the tortilla over the filling and cook for 2 minutes per side until the exterior is perfectly toasted and the cheese has completely melted.