1. In a small bowl, combine butter, lemon juice and parsley. Form a butter ball.
2. Wash tuna steaks and pat dry with paper towels. Season with salt on all sides. Put black pepper on a small plate. Coat tuna sides with black pepper, gently pressing it in.
3. Heat oil in a thick-bottomed frying pan over medium-high heat. Sear tuna steaks for about 2 minutes per side (or until the desired doneness is reached), turn off the heat and add butter mixture.
4. Spoon melted butter over the steaks and serve immediately.