Step 1

Stir together yogurt and pesto in a small bowl; set aside.

Step 2

Spread 1/2 tablespoon butter over 1 bread slice and place on a cutting board, butter-side down. Spread half of the pesto mixture on the bread; top with mozzarella, chicken, tomato and basil. Spread the remaining pesto mixture on the remaining bread slice and place, pesto-side down, on top of the basil. Top with the remaining butter.

Step 3

Place the sandwich in a medium nonstick skillet over medium heat; press down lightly with a spatula. Cook until the bread is toasted and the cheese has just begun to melt, about 90 seconds per side. Slice the sandwich in half diagonally and serve warm.