Step 1 Preheat oven to 180°C. Place couscous in a heatproof bowl. Add 1/4 cup boiling water. Cover and stand for 5 minutes. Stir with a fork to separate grains. Add almonds, parsley and red capsicum. Stir to combine.
Step 2 Using a small sharp knife, cut each roast lengthways, so that lamb sits flat, being careful not to cut all the way through. Divide mixture along centre of roasts. Roll up to enclose stuffing. Tie with string at 3cm intervals. Place on a baking tray. Spray with oil.
Step 3 Meanwhile, place eggplant, onion, zucchini and capsicum on a large baking tray. Spray with oil.
Step 4 Add both baking trays to oven. Roast lamb for 25–30 minutes for medium or until cooked to your liking. Roast vegetables for 30 minutes.
Step 5 Transfer lamb to a plate. Cover with foil. Set aside for 5 minutes. Slice lamb thickly.
Step 6 Add tomatoes to the vegetable pan. Roast for 10 minutes or until tender. Serve lamb with the vegetables and sprinkled with basil leaves.