Although a beautiful piece of sushi-grade tuna can be a rare treat, frozen tuna is a less expensive way to get the healthy omega 3 fatty acids tuna provides. Poaching the tuna in garlic-scented olive oil keeps it moist even when it needs to be served fully cooked. The tuna is not at all greasy and soaks up very little, if any, of the oil.
Thaw tuna if frozen. Dry with a paper towel. Remove skin or dark meat from the tuna, if desired. Cut into 1-inch cubes, making an even number of pieces for two equal servings. Sprinkle salt on the tuna cubes on at least two sides.
Choose a baking pan or dish that will allow the pieces to be about 1/4" apart from each other but without extra space. The pan should also be deep enough to allow it to be covered with a lid or foil without touching the tuna. Lightly oil the bottom of the pan or dish and evenly distribute the tuna.
Pour oil into the pan to come up 1/3" to 1/2" deep. Sprinkle the minced garlic (and thyme, if using) over the tuna in oil.
Cover and bake for 15 minutes (20 minutes if tuna is partially thawed). Turn the tuna pieces over. Cover and bake for a second 15 minutes for well-done but moist tuna.
Serve the tuna hot. Discard the oil and garlic (and loose thyme, if using).