Heat the olive oil in a deep pan over low heat. Stir in the garlic, ginger, diced green chili, and mustard seed. Slowly stir while the spices become fragrant and toasted. Then, stir in the cumin, curry powder, onion powder, chili powder, turmeric, and garam masala. Stir and heat until you can smell the warmed curry powder.
Stir in chopped eggplant and tomato with the salt. Fold the ingredients until the eggplant and tomato are covered in the spices. Put a lid over the pan and cook the ingredients over medium-low heat until the eggplant tenderizes – about 7 minutes. Occasionally stir the ingredients to avoid burning.
Pour the water into the pot. Leave the lid on and bring the curry to a simmer. Let the curry simmer for 10-15 minutes – until the eggplant is very soft but not mush. Turn the stove heat back down to low. Remove about ½ cup liquid and whisk the cornstarch into it. Then, return the thickened liquid to the curry. Simmer the curry without the pan lid until the curry thickens.
Serve 1 cup of the hot and spicy curry over a ¾ cup of cauliflower rice per serving.