This is a mild curry. To make it spicier, increase the ground red chili. You'll find all these spices at your local grocer or online at www.namaste.com.
Heat a large skillet over medium heat. Add the mustard and cumin seeds. Cook 2 minutes or until seeds are fragrant, stirring frequently. Combine the tomato and oil in a small bowl; add to the seeds. Cook 1 minute, stirring constantly.
Stir in the turmeric, red chili, and salt. Cook, stirring, for another minute.
Add chicken and cook for 1 minute. Stir in coconut milk; cover. Simmer over low heat 10 minutes or until chicken is cooked through.
Serve hot, spooned over warm basmati rice.