Heat vegetable oil over medium-high heat in a large, deep pan. Stir in mustard seeds and cook until seeds have been sputtering for 20 seconds; add cumin seeds. Stir in red chile and asafoetida. Add onion and fry for 2 minutes. Add garlic, bay leaf, ginger, and turmeric powder and cook for 2 minutes more. Stir in curry leaves, chili powder, and black pepper and cook until onions are golden brown, 5 to 7 minutes.

Add chicken to the pan and fry until almost cooked through, 8 to 10 minutes. Stir in coriander powder and mix well. Pour in coconut milk; bring to a boil. Add tamarind paste and salt; mix well. Add garam masala; reduce heat and let simmer, adding water as necessary, until curry reaches desired consistency and chicken is no longer pink in the center, about 10 minutes more.