Step 1: Prepare the Avocado Spread

1. In a small bowl, mash the avocado with a fork until smooth.
2. Mix in garlic powder, onion powder, salt, black pepper, and lemon juice. Set aside.

Step 2: Assemble the Sandwich

1. Spread a thin layer of mayonnaise or butter on one side of each bread slice.
2. Flip the bread over and spread Dijon mustard (if using) on the unbuttered side.
3. Layer one slice of cheese onto two of the bread slices.
4. Evenly distribute the shredded chicken on top of the cheese.
5. Spread the avocado mixture over the chicken.
6. Add spinach or arugula, red onion slices, and bacon bits (if using).
7. Place another slice of cheese on top before covering with the remaining bread slices, buttered side facing out.

Step 3: Cook the Sandwich

1. Heat a skillet or griddle over medium heat.
2. Place the sandwiches in the skillet and cook for 3-4 minutes on one side, pressing gently with a spatula.
3. Flip carefully and cook for another 3-4 minutes until golden brown and the cheese is melted.

Step 4: Serve and Enjoy

1. Remove from heat, let rest for a minute, then slice in half.
2. Serve warm with a side of chips, soup, or a fresh salad.