Prepare the Chicken:

• Season the chicken breasts with salt and pepper on both sides. This ensures the chicken is well-seasoned and flavorful.
• Heat the olive oil in a skillet over medium-high heat. This ensures the chicken cooks evenly and develops a nice sear, enhancing its flavor and texture.
• Cook the chicken breasts for about 6-7 minutes on each side, or until fully cooked and no longer pink in the center. A meat thermometer should read 165°F (74°C). This ensures the chicken is safe to eat and prevents any foodborne illnesses. Remove from the skillet and let rest for a few minutes before slicing thinly. Resting allows the juices to redistribute, making the chicken more tender and juicy.

Prepare the Avocado and Cheese:

• Slice the avocado and prepare the cheese slices. Set aside. This ensures the ingredients are ready for assembly, streamlining the sandwich-making process.

Prepare the Bread:

• Spread a thin layer of mayonnaise and Dijon mustard on each slice of bread. This adds moisture and flavor to the bread, preventing it from being dry and enhancing the overall taste.

Assemble the Sandwiches:

• On two slices of bread, layer the sliced chicken, avocado, and cheese. Add a few slices of red onion and tomato on top. This ensures the fillings are evenly distributed, creating a balanced and flavorful sandwich.
• Top each sandwich with the remaining slices of bread, mayo side down. This creates a secure sandwich and prevents the fillings from spilling out.

Grill the Sandwiches:

• Heat a skillet or grill pan over medium heat. Add a bit of butter or olive oil to the pan. This prevents sticking and adds a golden crust, enhancing the sandwich’s texture and appearance.
• Place the sandwiches in the skillet and cook until the bread is golden brown and the cheese is melted, about 3-4 minutes per side. Press down gently with a spatula to help the cheese melt evenly. This ensures the sandwiches are evenly cooked and the cheese is melted throughout, creating a gooey and satisfying bite.   
   

Serve:

• Remove the sandwiches from the skillet and let them cool for a minute before slicing in half. This allows the cheese to set slightly and prevents burning your mouth, ensuring a more enjoyable eating experience. Serve warm.