In a small bowl, mix the curry paste with cayenne, turmeric, and any other spices you like.
In a large, deep skillet, heat the vegetable oil over medium-high heat.
Add the chopped onions to the skillet and cook on medium heat for 2-3 minutes until they turn translucent.
Stir in the minced garlic and ginger, cooking for another 2-3 minutes until aromatic.
Add the prepared curry paste to the skillet, and stir it well to combine with the onions, garlic, and ginger.
Stir in the chopped tomatoes, 1 teaspoon salt, and a bit of brown sugar to intensify the flavors.
Reduce the heat to medium and let the curry mixture simmer for about 10 minutes, allowing the flavors to meld together.
Place the halibut fillets gently on top of the curry mixture, cover the skillet, and let the fish cook for about 7-10 minutes, depending on the thickness of the fillets.The halibut should be just cooked through and flake easily with a fork. Transfer the halibut curry to a serving platter and garnish with lime wedges.Enjoy your delicious Halibut Curry!