Prepare the base: Heat vegetable oil in a pan over medium-low heat. Add cumin seeds and onion pieces to build the foundation of flavor.
Add spices and seasoning: Incorporate Caribbean green seasoning, green scotch bonnet pepper (optional), smashed garlic, and fresh ground black pepper. Adjust heat to prevent burning.
Bloom the curry powder: Add your favorite curry powder to the pan, allowing it to toast in the oil and release its flavors.
Add the mackerel: Introduce the mackerel in tomato sauce to the pan, breaking the fish into large pieces. Rinse the can with about 3/4 cup of water and add to the pan.
Simmer: Bring the mixture to a boil, then reduce to a simmer, allowing the flavors to marry. Avoid adding salt due to the sodium content in canned mackerel.
Final touches: Add chunky pieces of tomato and cilantro. Finish with a splash of lime juice to brighten the dish and reduce the fishy scent.
Serve: Taste for salt and adjust if necessary. Serve the curry mackerel with rice, roti, or your favorite carbohydrate.