Heat 2 tablespoons oil in a large skillet over medium-high heat. Add halibut fillets; season with salt and pepper. Cook until flesh flakes easily with a fork, about 4 minutes per side. Transfer to a plate; cool until easily handled, about 5 minutes. Flake into small chunks.
Mix Italian cheese blend, egg, mayonnaise, onion, lemon juice, 2 tablespoons bread crumbs, Worcestershire sauce, garlic powder, dry mustard, and seafood seasoning together in a large bowl. Gently mix in flaked halibut.
Pour 3/4 cup bread crumbs into a shallow dish. Shape halibut mixture into 6 cakes and dip both sides in bread crumbs to coat.
Heat remaining 2 tablespoons oil in the skillet over medium-high heat. Add halibut cakes and cook until browned, about 5 minutes per side.