Bring the tuna to room temperature 10 minutes before cooking.
Warm a large nonstick skillet with oil over medium-low heat. Season the fish with salt and pepper. Raise the heat to medium-high. Place the tuna in the pan. Cook until brown on 1 side, about 4 minutes. Turn the fish over with a spatula, and cook until it feels firm to the touch, about 3 minutes more.
Transfer to a plate and serve as desired.
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