Pound the Chicken: Begin by placing the 1 large boneless skinless chicken breast between plastic wrap. Use a meat mallet or rolling pin to pound it flat until even in thickness. This helps the chicken cook uniformly.
Season the Chicken: In a small bowl, mix 1 tsp ground cumin, 1/4 tsp salt, and 1/4 tsp black pepper. Rub this seasoning evenly over both sides of the chicken breast.
Cook the Chicken: Heat 2 tbsp olive oil in a skillet over medium-high heat. Once hot, carefully place the seasoned chicken in the skillet. Cook for about 5 minutes on each side, or until the chicken reaches an internal temperature of 165°F. Remove from the skillet and let it rest before slicing.
Sauté the Onions: In the same skillet, add the sliced 1 medium white onion and sauté for approximately 7-8 minutes until soft and fragrant. Stir in 1/3 cup fresh cilantro, chopped, and 2 tbsp lime juice until combined, then remove from heat.
Assemble the Quesadillas: Preheat a cast-iron skillet over medium heat. On one side of a 8-inch flour tortilla, sprinkle 1/4 cup shredded mozzarella cheese, followed by some of the chicken (sliced), and then a generous portion of the onion-cilantro-lime mixture. Top with another 1/4 cup shredded mozzarella cheese and fold the tortilla in half.
Cook the Quesadillas: Place the prepared quesadilla in the skillet. Cook for 2-3 minutes on each side, or until golden brown and the cheese has melted. Repeat for the remaining tortillas and fillings.
Serve: Slice each quesadilla into quarters and serve hot. These quesadillas pair wonderfully with sour cream, guacamole, or a dash of hot sauce!