Preheat the grill or grill pan to medium-high heat (400°F).

Wash and slice the zucchini, red bell pepper, red onion, and portobello mushrooms into uniform ½-inch thick pieces.

In a medium bowl, combine sliced vegetables with half of the olive oil and balsamic mixture. Toss gently and let rest for 5 minutes.

In a small bowl, whisk together the remaining olive oil, balsamic vinegar, honey, minced garlic, sea salt, and black pepper to create the glaze.

Grill the vegetable slices for approximately 3-4 minutes per side until tender and charred.

Cut ciabatta rolls in half and brush the cut sides with the glaze. Toast on the grill for 1-2 minutes until golden brown.

Assemble the sandwiches with grilled veggies and mozzarella, then return to the grill for 2-3 minutes to melt the cheese.

Drizzle with remaining glaze and sprinkle torn basil leaves on top before serving warm.