Heat a saute pan on medium heat, add coriander seeds and dry red chilies. Toast them until fragrant and they start turning lightly dark in color. Remove from pan and set aside to cool. Once cooled, grind this into a coarse powder.
In the same pan; heat 1 tablespoon oil, add onions, garlic and ginger. Cook on medium flame, stirring frequently, until onions start to get lightly browned around the edges.
Next add tomatoes and cook until they are mushy. Remove from the pan and set aside. Grind into a smooth paste without adding any water.
In the same pan, heat the remaining 1 tablespoon oil, add mustard seeds and once they start to splutter, add the vegetables and mix well. Cover and cook till the veggies are tender, about 8~10 minutes.
Stir in turmeric and the ground masala powder. Mix well and cook for 1~2 minutes.
Next add the ground onion-tomato masala paste and cook for another 3~4 minutes. Stir in coconut milk, salt and garam masala. Mix well and bring the mixture to a boil. Curry is ready at this point, but if you think it is too thick for your liking, add more water and cook for couple more minutes.