Mash the avocado with a fork and mix in the lemon juice, salt, and pepper.
Prepare the garlic dressing by combining the dressing ingredients and blending with an immersion blender until smooth (I used a small food processor).
Spread avocado over 3 slices of bread. Top with tomato, drizzle with dressing, add the Muenster cheese, and top with the remaining bread slices.
Spread butter on the outside of the bread or grease a panini maker or waffle iron. Add the sandwiches and cook until the bread is golden and the cheese is melty.
Notes
Warning: this sandwich is a little messy when cooking. Let it cool for a minute or two before eating to minimize extra mess. There's plenty of avocado that you could stretch this across 4 sandwiches, if desired. I LOVED the extra avocado by making 3 sandwiches as written.
Nutrition Information
Serving size: 1 sandwich
Recipe by Hidden Fruits and Veggies at https://www.hiddenfruitsandveggies.com/2015/01/12/grilled-avocado-sandwich/