To turn this recipe into a main vegetarian meal, grill slices of halloumi or smoked tofu.
Cut the sweet potato or carrots into 1cm-thick slices. Put in a pan with enough water to cover, boil for 2 mins, then drain.
Heat the grill until hot. Line the rack with foil. Cut the courgette in half lengthways, then halve again for quarters. Slash the flesh in a criss-cross pattern.
Line up the potato or carrots, courgettes (cut-side up) and leeks and/or asparagus in the grill pan and brush with oil. Season, then grill on one side for 3-5 mins until browned and just softened – no need to turn. As they cook, remove to a heatproof dish.
Place the remaining vegetables and mushrooms (skin-side up) on the foil, brush with oil, season and cook for about 3-5 mins until softened and browned. Place in the dish and trickle over any cooking juices. Scatter over the nuts or seeds and return the dish to the grill for a minute or two so they lightly toast. Drizzle with a little vinaigrette and soy sauce just before serving.