Slice the flank steak against the grain into thin, bite-sized strips.
In a small bowl, whisk together the chili powder, cumin, sea salt, and black pepper.
Toss the steak strips with the spice blend until evenly coated.
Heat half of the avocado oil in a cast-iron skillet over medium-high heat.
Add the bell pepper and red onion, sautéing until they are tender and slightly charred.
Remove the vegetables from the skillet and add the remaining oil.
Sear the steak strips for 2-3 minutes until browned and cooked through, then deglaze with the lime juice.
Wipe the skillet clean and place the tortilla inside over medium heat.
Layer the cheese, steak, and vegetables on one half of the tortilla.
Fold the tortilla over and press down, cooking for 2 minutes per side until the exterior is golden and crispy.