Slice the flank steak into very thin strips against the grain and place in a small bowl.
Toss the steak strips with the chili powder, cumin, smoked paprika, sea salt, and black pepper until evenly coated.
Heat the avocado oil in a large non-stick skillet over medium-high heat.
Add the steak to the skillet and sear for 2-3 minutes until browned and cooked through, then transfer to a plate.
In the same skillet, add the sliced bell peppers and onions, sautéing for 4-5 minutes until tender and slightly charred.
Return the steak to the skillet, drizzle with lime juice, stir to combine, and then remove the entire mixture from the heat.
Wipe the skillet clean and place the tortilla inside over medium heat.
Sprinkle half of the cheese on one side of the tortilla, top with the steak and pepper mixture, and add the remaining cheese.
Fold the tortilla in half and cook for 2 minutes per side until the exterior is golden brown and the cheese is completely melted.