Pour 4 cups water in a bowl, add ¼ tsp turmeric powder. Cut brinjals into thin, long slices, add to the water and set aside.
Mix together red chilli powder, remaining turmeric powder, 4-5 tbsps mustard oil, dried mango powder and salt in another bowl.
Drain brinjal slices and add to the second bowl, mix well so that all the slices are well coated with the masala. Set aside to marinate for 5 minutes.
Heat 1 tbsp oil in a small non-stick pan. Add garlic, green chillies and walnuts and sauté till garlic turns golden.
Transfer the mixture into a mixer jar. Add mint leaves and lemon juice and grind into a chutney. Transfer the chutney into a third bowl. Add salt and mix well.
Heat the remaining mustard oil in another non-stick pan. Add the marinated brinjal slices, cover and cook, flipping sides till evenly golden.
Transfer the brinjal slices onto a plate. Spread the mint chutney and roll the slices.
Arrange the rolls on a serving plate, garnish with mint leaves and serve.