Pat the flank steak dry and slice it thinly against the grain. In a medium bowl, combine the sliced steak with onion powder, garlic powder, ground cumin, chili powder, salt, and black pepper. Toss to coat evenly.
Heat 1 tablespoon of olive oil in a large skillet or griddle over medium-high heat. Add the seasoned steak in a single layer (cook in batches if necessary to avoid overcrowding the pan). Cook for 2-3 minutes per side until browned and cooked through. Remove the steak from the skillet and set aside.
Wipe the skillet clean if needed. Reduce heat to medium-low. Place one flour tortilla in the skillet. Sprinkle about 0.5 cup of shredded Monterey Jack cheese over one half of the tortilla. Arrange a portion of the cooked steak over the cheese.
Fold the other half of the tortilla over the filling to create a half-moon shape. Cook for 2-3 minutes per side, or until the tortilla is golden brown and crispy, and the cheese is completely melted and bubbly.
Transfer the cooked quesadilla to a cutting board. Repeat with the remaining tortillas, cheese, and steak until all quesadillas are made.
Cut each quesadilla into 2-3 wedges and serve hot. Garnish with pico de gallo and sour cream, if desired.