Thinly slice the flank steak against the grain into bite-sized strips.
Heat the avocado oil in a large skillet over medium-high heat until it begins to shimmer.
Add the steak strips to the skillet and season with sea salt, black pepper, and chili powder.
Sear the steak for 3 to 4 minutes until browned and caramelized, then remove from the pan and set aside.
In the same skillet, add the sliced bell peppers and red onion, sautéing for 5 minutes until they are tender-crisp with slight char marks.
Place the whole wheat tortilla on a clean griddle or skillet over medium heat.
Spread half of the Monterey Jack cheese over one half of the tortilla, then layer on the seared steak and sautéed vegetables.
Top with the remaining cheese and fold the tortilla in half.
Cook for 2 to 3 minutes per side until the tortilla is golden brown and the cheese is completely melted.
Remove from heat, slice into wedges, and garnish with fresh cilantro before serving.