To make the sauce, mix yoghurt, garlic, lemon zest and juice in a small bowl. Set aside.
Heat the oil in a large nonstick frying pan and fry the onion for 2 - 3 minutes until soft; add the peppers and courgette and cook for 5 minutes until soft. Season well and remove to a large bowl and keep warm.
Mix mince, onion granules, garlic salt, and chilli powder in a large bowl. Lay the wholemeal wraps onto a board and press 1/4 of the meat mixture onto each tortilla. Spread it out thinly so it completely covers the tortilla.
Return a clean large nonstick frying pan to moderate heat, lay the tortillas into the frying pan meat side down, and cook one at a time for 5 minutes. Press down with a spatula to ensure the meat is evenly cooked.
Use the spatula to remove from the pan to a warm plate. Fill with warm vegetables and top with shredded lettuce, tomato and cucumber.
Drizzle yoghurt sauce and sriracha over the kebab, roll it up and eat immediately.