Heat oil in a skillet over medium heat. Saute shallots, tomato, and garlic until softened, 3 to 4 minutes. Add red chiles, coriander, cumin, mustard seed, turmeric, and black pepper. Cook and stir until a thick paste forms, 8 to 10 minutes. Pour in 2 cups water; add radish and season with salt. Simmer until small bubbles appear, about 7 minutes. Remove from heat; stir in green onions and cilantro.