Preheat grill to medium-high. Combine goat cheese, olives and onion in a medium bowl.
Mist zucchini slices on both sides with cooking spray and sprinkle with salt. Grill, turning after 4 minutes, until cooked through, 8 minutes total.
Mist one side of each tortilla with cooking spray. Place tortillas, oiled side down, on work surface. Sprinkle goat cheese mixture over half of each tortilla. Arrange zucchini and tomato slices in layers over cheese. Carefully fold tortillas over to enclose filling.
Turn heat to medium-low. Grill quesadillas, turning once, until cheese is melted and filling is heated through, 1 to 2 minutes per side. Cut into wedges and serve.