Place the tuna steak into a vacuum or ziptop bag and vacuum seal.
Heat the water bath to 108 degrees and place the tuna into the bath.
Cook in the water bath for at least 30 minutes and no longer than 1 hour.Use shorter times for thinner ahi steaks (i.e.under 1 inch) and longer times for thicker steaks.
Remove the tuna from the bag and pat dry.
Add salt and pepper to each side.
Heat the oil in a small cast iron or non-stick skillet over High heat until just starting to smoke.
Sear the tuna on each side for 30 to 45 seconds.
Use tongs to hold the ahi while searing the edges.
Plate the ahi and dress as desired.
Notes
I placed the ahi on a bed of quinoa and couscous to skip the cliche 'bed of rice'.
Recipe by Cooking 4 One at https://www.cooking-4-one.com/2017/02/27/sous-vide-seared-ahi/