Soaked red split lentils overnight for tadka dal. Proportion water to boil them in by weight? Any way to prevent the foam-up?
I cook red lentils in two ways: an excess of water and drain, or top up the water until they're done. In the latter case add any stock/wine etc. at the beginning, then top up with water from the kettle as necessary. This works for anything from lentil and tomato soup to dhal. It reduces foaming but doesn't eliminate it completely, turning the heat down to a low simmer and using a large pan are the best ways to prevent the foam escaping. I usually use a lid which helps a lot by reducing evaporation, but I tend to be quite a hands-on cook so topping up suits me. 

Red lentils don't need soaking, by the way (not that it does any harm).