Combine the rice wine vinegar, water, granulated sugar, kosher salt, and dried red chili flakes in a medium saucepan. Heat this mixture over high until it comes to a vigorous boil. This step is crucial for dissolving the sugar and salt effectively. Once the mixture reaches a boil, remove it from heat. Mix in the cucumber slices and give it a gentle stir to ensure they are thoroughly coated. Allow this to sit for about 10 minutes; this quick pickling process helps the cucumbers absorb the flavors beautifully. Transfer the marinated cucumbers to a sealable container and pop them in the refrigerator until you’re ready to serve—these will stay crisp and flavorful.

In a small bowl, whisk together the lime juice, soy sauce, minced ginger, sesame oil, honey, water, and garlic. Make sure to mix it until all the ingredients are completely blended. Set this bowl aside to let the flavors meld as we move on to cooking the tuna.

Place the sesame seeds on a flat plate. Next, using a paper towel, gently pat the ahi tuna fillets to remove any excess moisture—this will help the sesame seeds adhere better and form a nice crust. Dredge the tuna fillets in the sesame seeds, pressing them gently to coat evenly. Don’t worry if a few seeds fall off; just sprinkle more on top as needed.

Heat the grapeseed oil in a medium frying pan over medium-high heat until it’s shimmering—this is an indication that it’s hot enough. Carefully place the tuna fillets into the pan, making sure not to overcrowd them. Sear for about 1 minute until the sesame seeds are golden brown on the bottom. Gently flip the fillets and cook for another minute. Next, hold the edges of the tuna in the pan for about 15 seconds on each side to sear them lightly. Once the tuna is cooked, transfer it to a paper towel-lined plate to absorb any excess oil.

Using a sharp knife, slice the tuna into 1/4-inch thick pieces. Arrange these beautiful slices on serving plates. Don’t forget to serve them alongside your tangy pickled cucumbers and drizzle the soy ginger lime sauce on top or serve it on the side.