Preheat a chargrill on medium-high. Thinly slice zucchini diagonally. Spray with oil. Cook the zucchini for 1 minute each side or until tender and lightly charred. Transfer to a serving platter. Top with red onion, finely chopped, mint and coriander. Combine olive oil and lemon juice in a jug. Season with salt and pepper. Drizzle over the salad.