Mix tahina, yogurt, salt and fresh mint leaves in a small bowl and set aside. Marinate onion, zucchini, carrot and green capsicum with olive oil, lemon juice, mixed herbs, red chilli flakes and salt for about fifteen minutes. Grill the vegetables on a hot grill till the grill marks are seen on the pieces. Remove and set aside. Divide into four portions. Take one roti, apply the tahina mixture, arrange one portion of vegetables, sprinkle parsley and roll. Serve immediately.