Preheat the oven to 170°C.
Rub the lamb with olive oil and season with salt and pepper.
Cut small incisions in the lamb and insert rosemary pieces.
Place lemon and red onion slices in a roasting tin and set the lamb on top.
Cover with foil and roast for 3-4 hours, removing foil after 2 hours.
Remove the lamb from the tray and let it rest.
Deglaze the roasting tray with red wine over medium heat until reduced by half.
Whisk in flour then add stock and simmer for a few minutes.
Sieve the gravy into a saucepan and season.
Increase oven temperature to 190°C.
Mix aubergine, courgettes, onion, peppers, and garlic in a bowl and season.
Roast the vegetables in a clean tray for 25-35 minutes.
Stir basil leaves into the roasted vegetables.
Serve the torn lamb over the vegetables and drizzle with gravy.