One of the best kept secrets of Indian food is the way in which tomatoes are used. Outside of India, when using tomatoes we look for the juciest and sweetest around, often adding a pinch of sugar to dishes late in the season if the tomatoes are not as sweet as we desire them to be. In Indian cooking, it is the opposite. Tomatoes need to have some tartness to balance the spices used. It is considered a souring agent, along with others such as yoghurt, kokum, tamarind and lime/lemon.
While some recipes will call for peeled tomatoes, my preference is to blitz them in the blender, skin on, to form a puree, and use the puree in the recipe. This is quick and easy, and ideal for dishes such as dals, rasam, sambar and sauces.
This means that frozen tomatoes are ideal for use in Indian dishes. When tomatoes are plentiful and cheap, place your less ripe ones in ziplock bag and pop into the freezer for use during winter. You can also make purees and sauces in Late Summer or Autumn and freeze them for use during Winter and Spring.
If you need the texture of tomatoes in the dish, leave them in halves or chunks.