Roll the ahi tuna in the sesame seeds, pressing lightly so that the fish is evenly coated with sesame seeds on all side.
Heat the olive oil and sesame oil in a pan over high heat. Add 3/4 of the thinly sliced garlic to the pan and as the pieces turn golden brown, retrieve the garlic with a slotted spoon and set aside. Be careful not to burn the garlic. Add the tuna to the pan and sear the fish for about 15-20 seconds per side, then set aside on a plate.
Make the dressing by whisking together the ginger, soy sauce, lemon juice and remaining sliced garlic. Season to taste with salt and pepper.
Thinly slice the tuna, and divide between the plates. Drizzle the dressing over the tuna, then garnish with cilantro, scallion, chili and a drizzle of a little more olive oil.