Begin by generously seasoning the boneless skinless chicken breasts with salt and pepper. Heat a skillet over medium-high heat, adding a splash of olive oil. Cook the chicken for 6-7 minutes per side, or until the internal temperature reaches 165°F and no longer pink inside. Once cooked, remove from heat and let the chicken rest for a few minutes before slicing thinly.

While the chicken is resting, prepare the fresh toppings for your Chicken Avocado Melt Sandwich. Slice the avocado, cheese, red onion, and tomato into even pieces. Arrange these ingredients on a cutting board so they are ready to layer.

Take your favorite bread slices and spread a layer of mayonnaise and Dijon mustard on one side of each slice. Start layering your sandwich by placing the sliced chicken, followed by the creamy avocado, a generous portion of cheese, and then the crunchy red onion and tomato. Top it off with another slice of bread, spread side down.

In the same skillet or on a grill pan, add a small amount of butter or olive oil over medium heat. Carefully place the assembled sandwiches in the skillet, grilling them for about 3-4 minutes per side. Press down gently with a spatula to ensure even cooking until the bread turns golden brown and the cheese melts.

Once grilled to a crispy golden brown, remove the sandwiches from the heat and let them cool slightly. Slice each sandwich in half and serve warm.