Remove the tuna from the skillet and pat dry. Slice it 1/2 inch thick. Choose a deep glass or ceramic dish that will hold the tuna in a single layer. Lightly spread some of the sauce over the bottom of the dish. Add the tuna slices, laying them flat, and cover with the remaining sauce, spreading it evenly. Cover the dish with plastic wrap and let stand at room temperature for 6 hours, then refrigerate overnight. Bring to cool room temperature before serving.
Make ahead — The tuna can be refrigerated in the sauce for up to 2 days.
Rockport resident Heather Atwood writes the Food for Thought column weekly. Questions and comments may be directed to firstname.lastname@example.org. Follow her blog at HeatherAtwood.com.