Spray a griddle pan or skillet with cooking spray. Slice zucchini into thin slices lengthwise; making enough for each sandwich to have at least 2 slices.

Cook zucchini in hot griddle for 2-3 minutes, flipping once during cook time. Remove from heat and set aside.

Slice rolls open, drizzle with olive oil, sprinkle with salt and pepper, and place onto hot griddle pan.  Cook 1-2 minutes open, seasoned side down until they become toasted.

Fill each toasted roll with zucchini, a slice of tomato, and a slice of mozzarella.

Mix yogurt and pesto together and spread some onto each roll.

Close up the roll and slice in half. Serve with cubed watermelon on the side.