Pat the sirloin steak dry with a paper towel and slice it into thin, bite-sized strips.
In a small bowl, combine the chili powder, ground cumin, sea salt, and black pepper, then toss the steak strips in the seasoning until evenly coated.
Heat the olive oil in a large non-stick skillet over medium-high heat.
Add the sliced onions and bell peppers to the skillet, sautéing for 3 to 4 minutes until they are tender and slightly caramelized.
Remove the vegetables from the pan and add the steak strips, searing for 2 minutes per side until browned and cooked through.
Wipe the skillet clean and place the whole wheat tortilla in the center over medium heat.
Sprinkle the Monterey Jack cheese over one half of the tortilla, then layer the cooked steak and sautéed vegetables 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 exterior is golden brown and the cheese is fully melted.
Slice into wedges and serve immediately while the cheese is gooey.