Cajun seasoning should be liberally applied to both sides of the tuna steaks.
In a big skillet, heat the butter and oil over high heat until almost smoking.
Place the tuna steaks in the skillet and cook for 3 to 4 minutes, or until one side is browned. Cook for 3–4 additional minutes after flipping, or until desired doneness is reached. For medium-rare, a quick-read thermometer inserted in the center should register 140 degrees Fahrenheit (60 degrees Celsius).