Slice the flank steak against the grain into thin strips and season evenly with sea salt, black pepper, and ground cumin.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer.
Add the steak strips to the hot skillet in a single layer and sear for 2-3 minutes until deeply browned and cooked through, then transfer to a plate.
In the same skillet, add the sliced bell peppers and red onion, sautéing for 4-5 minutes until they are tender and show slight charred marks.
Wipe the skillet clean and return it to medium heat, then place the sprouted grain tortilla in the center.
Sprinkle half of the Monterrey Jack cheese over one half of the tortilla, then layer on the cooked steak and sautéed vegetables.
Top the filling with the remaining cheese and fold the tortilla in half, pressing down gently with a spatula.
Cook for 2 minutes per side until the tortilla is golden and toasted and the cheese is fully melted.
Remove from the heat, slice into three wedges, and garnish with fresh cilantro before serving.