Cut the tofu into 1 inch cubes. Cut any large mushrooms into quarters or in half. Small mushrooms can stay whole (about 1 inch wide). Cut zucchini in half the long way, and then into large chunks, about 1 inch.
Set up a charcoal grill and get the coals preheating.
Skewer each kabob alternating with tofu, zucchini and mushroom. You should be able to make about 10, depending on the length of your skewers and the size of your cubes.
Mix together the garlic powder, salt and black pepper. Spray the kabob with cooking spray and sprinkle with the seasoning mixture.
Grill on a hot grill until grill marks appear on the tofu and zucchini and the mushroom is softened, turning once.
Meanwhile, make the creamy chimichurri by combining parsley, garlic, dried oregano, salt and red pepper flake in a food processer. Process until the parsley is well chopped. Scrap the parsley mixture into the bottom of the bowl. Add the red wine vinegar and olive oil and process until the parsley is more finely chopped. Add the Greek yogurt, and process until just combined.