Thinly slice the flank steak against the grain into bite-sized strips.
In a small bowl, toss the steak strips with lime juice, chili powder, cumin, garlic powder, sea salt, and black pepper until evenly coated.
Heat a large non-stick skillet over medium-high heat with the avocado oil.
Add the red onion and bell pepper to the skillet, sautéing for 3-4 minutes until slightly softened and lightly charred.
Push the vegetables to the side of the pan and add the steak strips, searing for 2 minutes per side until browned and cooked through.
Remove the steak and vegetables from the pan and wipe the skillet clean with a paper towel.
Place the sprouted grain tortilla in the skillet over medium heat.
Sprinkle half of the Monterey Jack cheese on one side of the tortilla, then top with the steak and vegetable mixture.
Add the remaining cheese over the filling and fold the tortilla in half, pressing down firmly with a spatula.
Cook for 2 minutes per side until the tortilla is golden brown and the cheese is fully melted.
Slice the quesadilla into wedges and garnish with fresh cilantro before serving.