Thinly slice the flank steak against the grain into bite-sized strips.
In a small bowl, whisk together the lime juice, chili powder, cumin, garlic powder, sea salt, and black pepper.
Toss the steak strips in the marinade until evenly coated and let sit for 5 minutes.
Heat half of the avocado oil in a large non-stick skillet over medium-high heat; sauté the sliced bell peppers and onions until tender-crisp.
Remove the vegetables from the pan, add the remaining oil, and sear the steak strips for 2-3 minutes until browned and cooked through.
Wipe the skillet clean and place the tortilla in the pan over medium heat.
Sprinkle the cheese over one half of the tortilla, then layer on the cooked steak and sautéed vegetables.
Fold the tortilla in half and press down firmly, cooking for 2 minutes per side until the exterior is golden and crispy.
Slice into wedges and garnish with fresh cilantro before serving.