1To make marinade, juice 1 lemon and pour juice into a large bowl. Add oil, garlic and sugar. Season then whisk well. Transfer 1 tbs marinade to a small bowl. Set aside. Add mushrooms to remaining marinade, stir to coat. Cover and stand 15 minutes.
2Preheat barbecue plate on medium-high heat. Add mushrooms and asparagus and barbecue 3-4 minutes, turning once, until light golden and just tender. Remove to a bowl. Add prawns to the hot barbecue plate, spoon over reserved marinade and barbecue 2-3 minutes or until cooked through. Transfer to a plate. Half remaining lemon and barbecue halves cut-side down 3-4 minutes, or until golden.
3Add tomatoes and prawns to mushrooms and asparagus, toss gently to combine. Spoon onto a large platter, add spinach leaves and season. Drizzle with extra virgin olive oil and juice from barbecued lemons. Toss gently and serve with barbecue ?at bread.