Place yellow split peas in a saucepan with 2 cups water and bring to a boil. Reduce heat to medium-low, and cook until soft, about 15 minutes. In another saucepan, mix together the tamarind pulp stir in 1/2 cup water to make a watery juice. Bring to a boil over medium-high heat.
Add the bell pepper and tomato to the tamarind juice, and continue to boil until the vegetables are soft, and the liquid has reduced to almost half.
Meanwhile, grind the coriander seeds, yellow lentils, coconut and chilies to a paste using a mortar and pestle or food processor.
Add this paste to the tamarind sauce, then stir in the yellow lentils until everything is well blended. Bring to a boil once again, then remove from the heat and set aside.
Heat oil in a small skillet over medium heat, and add the mustard seed, cumin seed, and asafoetida powder. Once the mustard seeds start to sputter and the mixture is fragrant, remove from heat and stir into sambar.