Add oil, ginger, lime juice, rice vinegar and soy sauce to a medium mixing bowl. Whisk to combine then season with salt and pepper.
Set aside until ready to use. If the dressing separates by the time you are ready to use it, then whisk once again to combine.
For the seared tuna:
In a small bowl stir together the white and black sesame seeds until combined. Season the tuna with kosher salt then the sesame seeds so that it is completely coated in the sesame seeds.
Heat a large sauté pan or griddle over high heat, add the vegetable oil and heat through. Add the tuna to the pan and sear until no longer pink on each side, about 30 seconds each side for rare.
Remove the tuna to a cutting board and slice into ½” thick strips. The tuna should be seared in the outside but mostly raw on the inside.
To assemble:
Toss the arugula salad in about 2 tablespoons of dressing, adding more as desired. Scoop onto a plate and top with the seared tuna and avocado. Serve immediately.