Season the steak on both sides with the chili powder, ground cumin, sea salt, and black pepper.
Heat the avocado oil in a cast-iron skillet over medium-high heat until shimmering.
Sear the steak for 3-4 minutes per side for medium-rare, then transfer to a cutting board to rest for 5 minutes before slicing into thin strips.
In the same skillet, sauté the sliced red bell peppers and onions for 4-5 minutes until they are tender and slightly charred.
Wipe the skillet clean and return it to medium heat.
Place the tortilla in the pan and layer half of the cheese on one side, followed by the steak strips, sautéed vegetables, and the remaining cheese.
Fold the tortilla in half and cook for 2-3 minutes per side until the shell is golden brown and the cheese is fully melted.
Remove from the pan, drizzle with fresh lime juice, and garnish with chopped cilantro before slicing into wedges.