For the quesadillas
1 lb flank or skirt steak
2 teaspoons kosher salt
1 teaspoon onion powder
1 teaspoon black pepper
1/2 teaspoon ground cumin
1/2 teaspoon garlic powder
2 tablespoons olive oil, divided
1 medium onion, sliced
2 1/2 cups shredded mozzarella cheese
2 1/2 cups shredded monterey jack cheese
10 medium (8-inch) flour tortillas
For serving (optional)
Heat a large skillet over medium-high heat. While the skillet is heating up, pat steak dry on both sides with paper towels.
In a small bowl, combine salt, onion powder, black pepper, cumin, and garlic powder.
Sprinkle the seasoning evenly over both sides of the steak.
Add 1 1/2 tablespoons of olive oil to the skillet and add the steak. Cook on each side for about 4-8 minutes, depending on how thick the steak is and how “done” you want it to be.
Remove the steak from the skillet and transfer it to a cutting board to let it rest.
While the meat is resting, add the remaining 1/2 tablespoon of olive oil to the skillet. Add the sliced onions and cook, stirring occasionally, for about 8 minutes, until softened.
Transfer the onions to a bowl and carefully wipe off the inside of the skillet with a few paper towels until clean. Set aside.
Uncover the steak and slice it against the grain at an angle into thin slices or into bite-sized chunks.
In a medium bowl, combine the shredded mozzarella and monterey jack cheeses.
Assemble the quesadillas by adding 1/2 cup of shredded cheese to the bottom of one tortilla, followed by some steak, then onions, and one more 1/2 cup of shredded cheese. Sprinkle a pinch of salt and then top everything with one more tortilla.
Place the clean skillet back on the stove over medium heat. Using a spatula, carefully transfer the quesadilla to the skillet.
Cook the quesadillas for 1-2 minutes, or until the bottom of the quesadilla is golden-brown. Quickly flip over the quesadilla and cook for another 1-2 minutes, until golden brown and the cheese has fully melted.
Assemble and cook the remaining quesadillas.
Serve immediately as is, or cut the quesadillas into fourths. Serve with salsa, guacamole, and sour cream.