Creating the Grilled Balsamic Vinaigrette Sandwich Melt is a straightforward process. Follow these simple steps:

1. Preheat the Grill: Start by preheating your grill or a non-stick skillet over medium heat.
2. Prepare the Bread: Lightly brush one side of each slice of bread with olive oil.
3. Assemble the Sandwich: On the un-oiled side of two slices, layer the shredded mozzarella cheese, fresh spinach, tomato slices, and red onion. Drizzle with balsamic vinaigrette and sprinkle with salt and pepper.
4. Top It Off: Place the other two slices of bread on top, oiled side facing out.
5. Grill the Sandwich: Place the assembled sandwiches on the grill or skillet. Cook for about 3-4 minutes until the bottom is golden brown and the cheese starts to melt.
6. Flip and Cook: Carefully flip the sandwiches and grill the other side for another 3-4 minutes until golden brown and the cheese is fully melted.
7. Remove and Slice: Once done, remove the sandwiches from the grill and let them cool for a minute. Slice each sandwich in half to reveal the delicious fillings.
8. Serve Warm: Drizzle extra balsamic vinaigrette over the top if desired.

These steps will guide you in creating an incredible sandwich melt that is sure to impress!