Heat grill to medium.
Carefully thread the onion rounds onto skewers (this will keep them in tact as rounds while grilling), making sure the skewer goes through every onion ring.
Brush onions and courgette rounds with ¼ cup olive oil and season liberally with salt and pepper.
Grill vegetables 9-10 minutes each side, until nicely caramelized.
Cut the ciabatta loaf in half horizontally and lightly spray/brush with olive oil - transfer to the grill for 1-2 minutes until crisped.
Stir the ricotta with the lemon juice and zest, garlic, and basil leaves in a small bowl. Add salt and pepper to taste.
Spread ricotta over the bottom half and top with courgette and red onion slices.
Spread any remaining ricotta on the top half of the bread, place on top, and then cut into serving sizes (smaller for appetizer; larger for entree).
