Dice the tomatoes and gently press them with paper towels to remove excess moisture.
In a mixing bowl, combine tomatoes, red onion, basil, ½ tablespoon olive oil, salt, and black pepper.
Brush one side of every ciabatta slice generously with olive oil.
Turn half of the slices over so the oiled side faces down.
Layer mozzarella evenly over each slice.
Spoon the tomato mixture over the cheese.
Sprinkle generously with Parmesan.
Top with the remaining bread slices, keeping the oiled side facing up.
Press gently to hold the filling together.
Heat a griddle or frying pan over medium heat.
Cook the Bruschetta Grilled Cheese Sandwiches for about 3–4 minutes until golden brown.
Carefully flip and rub the toasted side with the garlic clove.
Continue cooking another 3–4 minutes until the mozzarella has melted completely.
Remove from the pan and lightly rub the second side with garlic.
Drizzle with balsamic glaze before serving.