Spicy eggplant curry

Ingredients

• 3 tablespoons oil
• 1 teaspoon black mustard seeds
• 1 medium onion, peeled and finely chopped
• 1 medium-hot red chilli, chopped
• 2 cloves garlic, peeled and finely chopped
• 1 teaspoon garam masala
• 1/2 teaspoon chilli powder
• 2 medium eggplants (about 600g total), cut into thick slices, then small chunks
• 1/2 cup canned crushed tomatoes
• 1/2 teaspoon salt
• 1/4 cup water
• 3/4 cup plain unsweetened yoghurt
• 1/2 cup chopped coriander