1. In a large wok or frying pan, combine oil, yellow split peas, and mustard seeds, if using, over medium high heat. Cover, if using mustard seeds, as they will pop, until you hear them crackle. Cook, stirring, until split peas are golden brown, 1 to 2 minutes.

2. Add gram beans and chiles. Carefully add curry leaves, if using, as they will splatter. Add cumin and cook, uncovered, stirring, for 1 minute.

3. Add asafetida, if using, and 1/4 cup coconut. Cook, stirring, for 30 seconds. Add green beans and 1 teaspoon salt; cook, stirring, for 5 minutes.

4. Add remaining 1/4 cup coconut, the saambhar or rasam powder, if using, and 1 cup water. Bring to a simmer, cover, and cook until beans are tender, about 10 minutes.

5. Uncover and cook, stirring frequently, until all of the water has evaporated, about 5 minutes more; season with salt. Serve immediately.