Aloo baingan ki subzi - potato and eggplant in tomato gravy

Ingredients

• 6-8 small eggplants unpeeled and cubed
• 2 medium size potatoes peeled and cubed
• 1 tomato chopped
• 1 red onion finely chopped
• 2-3 green chillies slit lengthwise
• 2-3 cloves of garlic finely chopped
• 1/2 teaspoon mustard seeds
• 1/2 teaspoon turmeric powder
• 1 teaspoonred chilli powder
• 1 teaspooncumin-cilantro powder
• salt to taste
• 2 tablespoons olive oil