Finely grind fenugreek seeds in an electric coffee/spice grinder.

In a small bowl, stir together ground fenugreek with vinegar, ground coriander, ground cumin, cayenne, and turmeric.

Rub the spice mixture all over the salmon fillets in a shallow baking dish.

Cover the dish and marinate the salmon at room temperature for 30 minutes.

While the salmon is marinating, cut the bell peppers into thin strips, thinly slice the onion, and finely chop the garlic.

Heat 1 1/2 tablespoons of vegetable oil in a 10- to 12-inch nonstick skillet over moderately high heat until hot.

Sear the salmon fillets until golden, about 2 minutes on each side. Transfer the salmon to a plate.

Add the onion, garlic, gingerroot, and 1 1/2 tablespoons of oil to the skillet.

Cook over moderate heat, stirring occasionally, until the onion is lightly browned.

Stir in the coconut milk and salt, then bring the sauce to a boil, stirring.

Add the salmon fillets and gently simmer until they are just cooked through and the sauce has thickened, about 5 to 6 minutes.

In another skillet, heat the remaining tablespoon of oil over moderately high heat until hot.

Sauté the bell peppers, stirring, until crisp-tender and lightly browned, about 5 to 6 minutes.

Serve the salmon and sauce over cooked rice, topped with the sautéed bell peppers.