Wash the red lentils at least 3 times in warm water until the water comes out clear. Place in a large pot with 1.5L of water and boil for 15 minutes.
Blend the chopped tomatoes in a hand blender.
In a mortar and pestle, bash 4cm of ginger, 4 cloves garlic and 2 tsp of chilli powder to form a thick paste.
In a large pan, pour two glugs of vegetable oil and heat on medium. Add in the black mustard seeds and cumin seeds. Once they start bubbling add in the chopped tomatoes. Quickly pop a lid on - they will spit out so be careful.
Add in the turmeric, cumin powder, coriander powder, 2 tsp of chilli powder, 2 tsp of salt and the pounded garlic and ginger paste. Cook on a medium heat for 10 minutes, stirring frequently.
Thinly slice 6 cloves of garlic and the green chilli, finely chop the coriander and chop 4cm ginger into matchsticks.
For the garlicky oil, heat up 50ml of vegetable oil in a small pan and gently cook the thinly sliced garlic and curry leaves until golden.
To check if the dhal is cooked, press a few grains between your fingers to feel if they are tender. Drain the dhal and add it into the curried tomatoes. Add in 250ml of water and continue cooking for 2 minutes. Season to taste and stir in ¾ of the coriander.
Pour over garlicky oil over the dhal and put a lid on to allow the garlic flavour to infuse through.
Finish with the remaining ginger, chopped chilli and coriander and serve with a big bowl of rice or just on its own.