Step 1Wash the channa dal well, picking through and removing any dark pieces. Bring the water to a boil in a saucepan and add salt to taste. Add the channa dal, return to boil, then reduce the heat to simmer and cover. After 40 minutes, add the cabbage, bell pepper and turmeric. Continue cooking until the dal is thoroughly cooked and soft, about 1 to 1 1/2 hours longer.
Step 2Heat the oil in a skillet over medium heat. Add the mustard seeds, curry leaves and chiles and cook until fragrant, about 1 to 2 minutes, reducing heat if necessary to avoid splattering. Stir the spices into the soup and serve.