Take spinach and onions with 1 cup of water in a saucepan; cover and cook on medium heat for about 5 minutes.
Add green chilies, salt and tamarind juice (add ¼ cup water to tamarind pulp to make the juice); cook for 10minutes.
In the mean time, mix the flour with ¼ cup water to make slurry with no lumps. Add this to the spinach mixture and cook for another 5 minutes till the mixture is slightly thickened.
Remove from heat and add the tadka or tempering. For tempering, heat 1 tsp oil in a small saucepan, add all the ingredients listed, let the seeds splutter. Add this to the spinach mixture. Serve with rice.