Slice the flank steak into very thin strips against the grain and season evenly with sea salt, black pepper, ground cumin, and garlic powder.
Thinly slice the poblano pepper and red onion into strips.
Heat the avocado oil in a large non-stick skillet over medium-high heat.
Add the poblano peppers and onions to the skillet, sautéing for 4-5 minutes until they are softened and show slight charred edges.
Push the vegetables to the outer edges of the pan and add the steak strips to the center, searing for 2-3 minutes until browned and just cooked through.
Remove the steak and vegetable mixture from the skillet and set aside on a plate.
Wipe the skillet clean and place the tortilla in the pan over medium heat.
Sprinkle the Monterey Jack cheese over one half of the tortilla, then layer the steak and vegetable mixture on top of the cheese.
Fold the tortilla in half and press down gently with a spatula, cooking for 2 minutes per side until the tortilla is golden brown and the cheese is fully melted.
Slice into wedges and serve immediately.