PREP: If using uncooked tortillas, warm them in a skillet according to package directions and set aside. (These tortillas need to be cooked through before assembling quesadillas regardless of what cooking method (skillet or air fryer) is used.) If using already cooked tortillas, no prep is needed there. Dice onion and red pepper. Finely chop cilantro. Grate cheese.
BEEF: Add the olive oil to a large skillet over high heat. Once oil is shimmering, add onion and red pepper. Sauté until golden, about 3-5 minutes. Push veggies to the side and add the ground beef to the center of the pan. Let beef sear (brown) before crumbling with a wooden spoon and browning all the way through. (Drain/remove any grease if needed.) Reduce the heat to medium and add in the seasoning mix, tomato paste, water, and garlic. Stir until very fragrant, about 1-3 minutes. Remove from heat and then add in the frozen corn and cilantro. Mix through.
ASSEMBLY: Divide cheese and meat filling among 6 tortillas (on one side of each tortilla). Sprinkle 2 tablespoons of cheese on one-half of the tortillas. Add a heaping 1/2 cup ground beef on top and then sprinkle another 2 tablespoons cheese over that. Press together.
SKILLET: Use a pastry brush to coat both sides of the quesadillas with some oil (or use cooking spray). Add 2 quesadillas at a time to a dry non-stick skillet over medium-low heat. Cover skillet with a lid and cook for about 2-3 minutes or until golden brown and crispy. Remove the lid, carefully flip the quesadilla and press down lightly with a spatula to seal the edges. Cook, uncovered for another 2-3 minutes or until crispy, browned, and cheesy filling has melted. It's important to keep the heat low so the cheese can melt before the tortilla browns too much (reduce heat if tortilla is browning before cheese is melted). Repeat this process to finish cooking all the quesadillas (See Note 4).
AIR FRYER: Stick toothpicks through the center edge of the quesadillas. Generously spray both sides of the quesadilla with cooking spray. Place 2 quesadillas in the air fryer insert, giving each plenty of space. Cook at 350 degrees F for 6-8 minutes, flipping halfway through or until quesadillas are crisp, golden, and the cheese is melted. (Note 6) Before flipping, press the quesadilla close together to seal the edges. Quesadillas have the tendency to open even with toothpicks. Remove carefully from the air fryer and let cool a couple minutes before cutting and serving. Repeat the process to finish cooking all the quesadillas (See Note 4).
SERVE: Once quesadillas are cooked, cut into wedges and serve with guacamole, sour cream, salsa. etc. Enjoy!