Pat the flank steak dry and slice into thin strips against the grain.
In a small bowl, whisk together chili powder, smoked paprika, cumin, sea salt, and black pepper.
Toss the steak strips with the spice blend and half of the lime juice until evenly coated.
Heat avocado oil in a large cast-iron skillet over medium-high heat.
Add the steak and sear for 3-4 minutes until browned and cooked through, then remove from the pan.
In the same skillet, sauté the bell peppers and red onions for 3 minutes until tender-crisp.
Wipe the skillet clean and place the tortilla in the center over medium heat.
Sprinkle the cheese over half of the tortilla, then layer the steak and sautéed vegetables on top.
Fold the tortilla in half and cook for 2 minutes per side until the exterior is golden and the cheese is melted.
Slice into wedges and serve with a dollop of Greek yogurt, fresh cilantro, and the remaining lime juice.