1. In a large bowl, cover the lentils with 2 inches of tepid water. Stir in 1 teaspoon turmeric and the fenugreek seeds. Set aside for 1 hour.

2. Drain the lentils and transfer to a small saucepan. Add enough water to cover by 2 inches and bring to a simmer over medium heat. Cook until the lentils are tender, 30 to 40 minutes. Turn off the heat and purée the lentils in batches in a blender or food processor until smooth.

3. In a large soup pot set over medium-high heat, heat the oil and mustard seeds. Once the mustard seeds start to pop, about 2 to 3 minutes, add the dried chile and curry leaves. Fry for 10 seconds, then stir in the remaining 1 tablespoon turmeric, the chile powder, sambhar masala and the onions. Reduce the heat to medium and cook until the onions are soft, stirring often and scraping up browned bits from the bottom of the pan, 4 to 5 minutes. Stir in the tomato paste and cook, stirring often, until the paste darkens, 3 to 4 minutes. Stir in the tamarind paste, salt, vegetable broth and puréed lentils. Increase the heat to medium-high and bring to a simmer.

4. Add the carrots and cook until tender, 8 to 10 minutes, then add the cucumber balls, cherry tomatoes, radishes and peas. Cook until the raw vegetables are warmed through, 1 to 2 minutes. Turn off the heat, add the cilantro and serve.