Preheat the oven to 400℉ and prepare a baking sheet with parchment paper.
In a small bowl mix together the cumin, garlic powder, onion powder, 1 tsp kosher salt, 1/2 tsp black pepper, and 1 tsp chili powder.
Pat the flank steak dry and brush with 1 tbsp olive oil. Rub the spice mix onto both sides of the steak and place it on the parchment-lined baking sheet.
Place the peppers and onions into a large bowl and toss with 1 tbsp olive oil, 1/2 tsp kosher salt, and 1/2 tsp black pepper. Arrange the peppers and onions around the steak on the baking sheet.
Place the baking sheet in the oven and cook, turning the steak over halfway through. Cooking time will depend on how well done you like your steak and the thickness. Medium rare will be about 12-15 minutes of cook time. Add more for medium or well done.
Remove from the oven and let it stand 5 minutes before slicing the steak.
To serve, place sliced steak, peppers, and onions in a warmed tortilla and top with cheese, cilantro, and salsa.