Cut tuna into square pieces, about 1-inch size, set aside.
In a large bowl stir together first five ingredients through ginger until combined. Remove half of the marinade and set aside.
Toss tuna pieces into half of the marinade to coat. Marinade about 20 minutes covered in the fridge.
Evenly spread sesame seeds onto a plate or flat surface. Coat each piece of tuna with seeds. For best presentation, coat 4 adjacent sides, but leave the two opposite ends uncoated to keep meat exposed.
Heat olive oil in a large non-stick pan to medium-high heat. Add prepared tuna pieces and cook each sesame-coated side until lightly browned, about 15-20 seconds per side. Centers should be pink and rare.
Remove from pan and insert one toothpick into each. Serve with remaining sauce for dipping.
Start with fresh, sushi quality ahi tuna (see section above in the post for more details on finding fresh fish)
Purchase tuna steaks that are about 1-inch thick so you can cut into squares
Use liquid aminos instead of soy sauce for gluten-free, but the flavor will be different
Reserve some of the marinade (not added to fish) for dipping
If you don't like raw fish and prefer to cook it to medium, sear it about 1-2 minutes on each side.