Begin by washing and patting dry your zucchini, red bell pepper, red onion, and portobello mushrooms. Slice the zucchini lengthwise and the other vegetables into uniform ½-inch thick pieces.

In a mixing bowl, drizzle half of the olive oil and balsamic vinegar over the sliced vegetables. Add a pinch of sea salt and black pepper, then toss everything together until all pieces are evenly coated. Allow this mixture to sit for about 5 minutes.

In a small bowl, whisk together the remaining olive oil, balsamic vinegar, honey, minced garlic, and a sprinkle of salt and pepper for the glaze. Set aside for drizzling later.

Preheat your grill or grill pan to medium-high heat, aiming for around 400°F.

Carefully place the marinated vegetables on the grill, cooking each side for about 3-4 minutes. Add the ciabatta rolls cut side down for the last 1-2 minutes to toast.

Once grilled, remove the vegetables and toasted ciabatta rolls from the grill. Layer the grilled veggies on one half of the bread, add mozzarella, and drizzle the remaining balsamic glaze before topping with the other half.

Return the assembled sandwiches to the grill for 1-2 minutes, grilling until the bread is crispy and the mozzarella is melty.

Slice the sandwiches in half and serve warm, alongside a fresh salad or sweet potato fries.