Combine the water with the lentils in a pot large enough to hold the ingredients plus some extra room. Lentils can boil over if you don't watch them closely...
Bring the water and lentils to a boil, uncovered and then reduce heat to low, cover and simmer until the lentils completely lose their shape. This takes about 40 minutes.
While the lentils cook, heat 3 Tbsp oil in a frying pan over medium heat. Add the mustard seed and panch phoran. Wait for them to start to crackle. This takes 20-30 seconds.
Add the onions and minced green chili, reduce heat to medium low and cook until the onions soften and turn translucent. This takes about 8-10 minutes.
Increase the heat to medium and add the garlic ginger paste. Stir into the onion chili mixture and cook for about a minute.
Add the paprika and 1 tsp salt. Stir to mix evenly and cook another minute or so.
Add the tomatoes and cook, stirring frequently, until the tomatoes soften. You know you are done when the skin starts to come off the tomato.
Fold the tomato mixture into the lentils. Stir to combine. Taste and adjust the salt. You will probably need another 1/2 tsp or so. Creep up on it, adding a bit at a time. You can add salt. You cannot take it away.