In a small bowl, combine melted butter with olive oil and sea salt, lemon juice, and zest. Stir to combine.

In a separate bowl, combine salt, paprika, garlic powder, onion powder, and black pepper.

Evenly sprinkle spice mixture onto both sides of fish fillets.

In a large, heavy pan over medium-high heat, heat olive oil until hot. Cook 2 fish fillets at a time to avoid overcrowding, which allows for even browning. Cook each side 3 to 4 minutes just until fish becomes opaque, feels somewhat firm in the center, and is browned.

Lightly drizzle some of the lemon butter sauce as you cook, reserving the rest for serving.

Serve fish with remaining lemon butter sauce, cilantro, and lemon slices.