In a small bowl, mix the avocado with the lemon juice and salt. Set aside.

Butter both slices of bread on one side and put together (butter sides together). Then you can build your sandwich on top of the non-buttered side facing up.

Layer ingredients in this order: 1 slice of cheese on the bread, 2 tomato slices, half smashed avocado, and another slice of cheese.

Repeat with remaining ingredients for second sandwich.

Heat a saute pan or panini maker over medium-low heat.

Lift up layered bread and place in heated pan or panini maker then place second piece of buttered bread on top (buttered side up).

When the bottom piece of bread is slightly browned, flip over and continue to grill until both sides are golden brown and the cheese is melted. If using a panini maker you won't need to flip it.

Remove the sandwich from the pan and repeat grilling for second sandwich.