Preheat your grill to medium-high heat, around 400°F. Wash and slice the zucchini, red bell pepper, and eggplant into ½ inch thick slices.

In a large bowl, toss sliced vegetables with olive oil, balsamic vinegar, salt, and pepper. Marinate for at least 30 minutes.

Once the grill is hot, grill the marinated veggies for 4-5 minutes on each side until tender with grill marks.

Spread pesto on one side of each slice of bread. Layer grilled veggies, fresh spinach, and mozzarella cheese.

Brush the sandwich's outer sides with olive oil and grill for 3-4 minutes per side until toasted and cheese is melted.

Let cool for a minute before slicing. Garnish with fresh basil leaves before serving.