Start by spiralizing your cucumber. Since mine was a large cucumber, I ended up cutting it in half to make it a bit easier. I spiralized the cucumber with Blade A. Really B or C would be fine, too. Set the cucumber noodles aside.
In a medium bowl, whisk together the rice wine vinegar, sesame oil, zested garlic clove, red pepper flakes and a 1/2 teaspoon of salt. Add the spiralized cucumber to the medium bowl and toss until thoroughly coated. Set aside.
To a small plate, spread out the sesame seeds and lightly mix in a few pinches of salt. Add the tuna to the plate and coat it thoroughly with sesame seeds. In a small skillet, set over medium-high heat, add a few tablespoons of olive oil. When the oil is hot, add the tuna and cook on one side for about a minute seconds; flip the tuna over and cook on the opposite side for an additional minute. Transfer to a cutting board and cut the tuna into slices.
To assemble, divide the noodles amongst two bowls. Top with the slices of tuna and a few leaves of cilantro.