Heat the pastrami in the microwave unitl warm.
Take a slice of bread and spread with butter, set aside. (If making 2 sandwiches butter 2 slices of bread).
Take another slice of bread and spread it with 1/4 of the garlic aioli.
Place 2 slices of Swiss cheese on top of the aioli.
Take half of the warm pastrami and add it to the sandwich.
Take another 2 slices of Swiss cheese and place on top of the pastrami.
Take the bread that has butter on one side, and spread the garlic aioli on the other side. Place that slice of bread with the buttered side on top of the sandwich, with the buttered side on the outside.
Put the buttered side of the sandwich down in a skillet. Butter the side that is facing up.
Over medium heat grill the sandwich for 4 to 5 minutes or until the bread is browned and the cheese is melted. Flip and continue to grill the other side for another 4 to 5 minutes until the bread is browned and the cheese is melted.
Serve immediately.