Spread the outer side of each slice of bread with 1 tablespoon butter.
Lay the bread slices in the pan, buttered side down, and layer two of the bread slices with a single layer of mozzarella cheese, and the other two slices of bread with the brie.
Add the thinly sliced chicken to the mozzarella layers, and grill the bread slices for 4-5 minutes, until the bread is toasted and golden brown, and the cheese has melted.
Flip one slice of bread on to the other to create a sandwich, then place a lid on the pan for one minute, if the cheese needs additional melting. Serve and enjoy!