Warm your oven to 220°C/Fan 200°C/Gas 7. Scrub the sweet potatoes and slice them into bite-size pieces. Trim the aubergines and cut them to match. Tumble the sweet potatoes and aubergines into a large roasting tin and toss with 1 tbsp olive oil and a little salt and pepper. Slide into the oven to roast for 25 mins, turning once, till caramelised and tender.
Meanwhile, put a small frying pan on a medium heat and tip in the peanuts. Toast for 2-3 mins till browned, then tip onto a plate. Set aside to cool a little, then roughly chop the peanuts.
Thinly slice the chilli (you can halve it and scoop out the seeds and pith for less heat) and slide it into a large bowl. Peel and grate in the garlic and ginger. Grate in the lemon zest and squeeze in the juice. Add 2 tbsp tamari and 1 tbsp olive oil. Peel and thinly slice the red onion. Add the onion to the dressing and stir together. Set aside.
When the veg have roasted, add them to the bowl with the onion. Add the toasted peanuts and fold through the lamb's lettuce. Divide the salad between 2 plates and serve.