Combine all Seasonings ingredients ( Onion Powder through Cayenne Pepper) in a small bowl.
Pat fillets dry with paper towels. Season the fillets liberally with Cajun Seasoning on both sides, pressing the seasoning into the fish with your hands.
Place a large saute pan over medium-high heat and add butter and oil. When the fat is nice and hot, add the seasoned fish. Cook, undisturbed, for several minutes, until golden brown on one side. Flip fish over and continue to cook until opaque and completely cooked through.
Squeeze lemon juice over the fish (optional) and serve.