Use paper towels to thoroughly dry excess moisture from 4 halibut fish fillets.
In a bowl, combine 2 tbsp melted butter, lemon juice and zest from 1 lemon, and 11/2 tsp kosher salt. Stir to combine. In a separate bowl, combine 1/2 tsp kosher salt, 1 tsp paprika, 1 tsp garlic powder, 1 tsp onion powder, and 1/4 tsp black pepper. Evenly press spice mixture onto both sides of fish fillets.
In a pan over medium-high heat, heat up 3 tbsp oil until hot. Cook 2 fish fillets at a time to avoid overcrowding. Cook each side just until fish becomes opaque, feels somewhat firm in the centre, and is browned - lightly drizzle some of the lemon butter sauce as you cook, reserving the rest for serving.