How to Make It
In a large pot, cover the chicken breasts with water. Bring to a gentle simmer and cook for 15 to 20 minutes, or until cooked through. Remove the chicken from the water and let cool. Cut the chicken into bite-size pieces, season with salt and pepper and set aside.
Spread half of the cheese on top of 4 tortillas. Top with the chicken and red onions. Add a final layer of cheese and gently spread the filling evenly around each tortilla. Top with the remaining tortillas.
Heat a large skillet or griddle over medium-high heat. Place a filled tortilla on the pan, and cook the tortilla for about 3 minutes or until the bottom is golden. Carefully flip the quesadilla and cook for another 2 to 3 minutes until the second side is golden and the cheese is completely melted.
Remove from the pan and repeat with the remaining quesadillas. Allow each to cool for a few minutes before cutting into 4 to 6 pieces.