In a bowl, mash the avocado with lime juice and salt until creamy but slightly chunky.
Fold in diced tomato, minced red onion, and chopped cilantro to make fresh guacamole.
Butter one side of each sourdough bread slice.
Place two bread slices, butter side down, on a skillet heated over medium heat.
Spread a generous layer of guacamole on each bread slice in the skillet.
Top each with sliced turkey breast and two slices of sharp cheddar cheese.
Cover with the remaining bread slices, butter side up.
Grill sandwiches for about 4-5 minutes on each side until the bread is golden brown and cheese is melted.
Remove from skillet and let rest for 1 minute.
Cut sandwiches diagonally in half and stack halves slightly offset on a white rectangular plate.