Toast the bread slices until golden and crisp.
Prepare the Chicken:
Cook the chicken breast if using raw, then slice thinly.
Assemble the Sandwich:
On one slice of toasted bread, layer avocado, tomato, and sliced chicken.
Top with a slice of Swiss cheese.
Spread mayonnaise or mustard on the other slice if desired.
Melt the Cheese:
Place the sandwich under the broiler for 1–2 minutes until the cheese is melted and bubbly.
Serve:
Serve warm with a side of fresh salad or sweet potato fries.
