Wash the spinach leaves and drain the water, keep aside.
Peel and chop the onion, keep it separate from the spinach.
Chop the tomatoes too in medium sized pieces and you can keep this aside with the spinach leaves.
Heat oil in the pressure cooker and add the mustard seeds to make the seasoning.
When the mustard seeds splutter, add the red chilies and fry for a few seconds.
Add the chopped onion and saute for about 2 minutes.
Add the salt, spinach leaves and chopped tomatoes and mix well and saute for another 1 minute.
Wash the yellow pigeon peas (toor dal) in water 2 to 3 times and add to the cooker and mix well.
Add the water and spice, mix everything well and close the pressure cooker with the lid (and safety valve).
Cook in medium heat for about 10 to 12 minutes or for 4 whistles.
After 10 to 12 minutes of cooking, switch off the stove and wait for the pressure cooker to cool down.
Once the cooker is cooled enough, open the cooker and see if the dal (pigeon peas) and vegetables are cooked enough as needed. In case you think the gravy is less, you may add a little more water and heat for another 1 minute.
Mix the contents very well and the spinach sambar is ready to serve!
Serve the sambar with rice for lunch or dinner or you can serve the sambar for dosa or idli for breakfast, snack or dinner as you wish!