Wash onion and tomato.Chop onion in slices and tomatoes in small pieces and keep them aside.
Cut cauliflower in big pieces and potato in small pieces. Wash and drain the water out. Keep all the dry spices separately in a plate.
Heat oil in a pan at medium heat. Add cumin seeds and let them cook for few seconds. Now add sliced onions, saute and cook till onion turns little pink.
Now stir in grated ginger garlic. Mix and cook for another minute or till the raw smell of ginger garlic is gone.
Now add turmeric powder. Mix and add chopped tomatoes. Saute and cover the tomatoes for few minutes till they become mushy.
Once tomatoes are mushy and release oil add chilly powder, cumin powder, coriander powder, garam masala and salt.
Give it a nice mix and add potato (aloo) and cauliflower (gobi) pieces. Saute and cook aloo gobi for 8-10 minutes without cover. Saute them couple of times in between to avoid sticking or burning.
Now reduce the heat to medium low, cover and cook for almost 15 minutes or till potatoes are fork tender.
Once veggies are cooked add green chillies and fine chopped coriander leaves. Serve this dry aloo gobi with chapatti or dal rice.