Begin boiling water for rice, and cook according to package directions.
Set flame to medium. Add olive oil to skillet, and heat until the oil begins to ripple. Add the garam masala and onion, and sauté for 3-4 minutes, until the spices are fragrant and the onion has softened.
Add red pepper flakes, salt, and the can of tomatoes. Cook 4-5 minutes, until tomatoes are simmering.
Add the sardines (with the tomato sauce) and the coconut milk. Bring to a simmer, and then squeeze half the lime juice into the curry.
Add more salt if needed, and more red pepper flakes if you'd like it to be spicier.
Quarter the remaining lime half. Serve the curry with the rice and a lime wedge. Optionally, serve with a few sprigs of cilantro.
Recipe variation: To useregular, unflavored canned sardines, add 2 TB tomato paste, and 2 tsp smoked paprika.