Slice the flank steak against the grain into very thin strips and place them in a small bowl.
In a small ramekin, combine the chili powder, smoked paprika, cumin, sea salt, and black pepper, then toss with the steak to coat evenly.
Heat a large non-stick skillet over medium-high heat with half of the avocado oil.
Add the sliced bell peppers and red onions to the pan, sautéing for 3-4 minutes until softened and slightly charred, then remove them from the pan and set aside.
Add the remaining oil to the same pan and sear the steak strips for 2 minutes per side until browned; stir in the lime juice and fresh cilantro at the very end.
Wipe the pan clean and place the tortilla inside, sprinkling half of the cheese over one side.
Layer the cooked steak and sautéed vegetables over the cheese, then top with the remaining cheese and fold the tortilla in half.
Cook for 2 minutes per side until the tortilla is golden brown and the cheese is fully melted.
Slice into wedges and serve immediately.