In a food processor, pulse garlic and walnuts until finely chopped. Add fresh basil leaves, grated vegetarian parmesan cheese, and a pinch of salt and pepper. Gradually drizzle in extra virgin olive oil while blending until smooth and creamy, about 30 seconds.

Slice ripe tomatoes and fresh mozzarella into thin rounds. In a bowl, combine tomatoes, mozzarella, and baby spinach. Drizzle with reserved olive oil and balsamic reduction, sprinkle with salt and pepper, and toss gently.

Lightly warm ciabatta rolls for 2-3 minutes if desired. Spread basil pesto on one side of each slice of bread. Layer the filling evenly on one slice and close with the other slice.

Slice the sandwich into quarters using a sharp knife. Serve immediately or let flavors meld for a couple of minutes before serving.