Prep Time: 20 minutes
In a small bowl, combine the lemon juice, miso paste, rice vinegar, honey, and sesame oil. Use a fork to stir briskly, until the miso and honey is dissolved. Taste and adjust for preferences. In a large mixing bowl, toss Salad Mix with dressing, massaging slightly. Add citrus slices, cover and refrigerate while cooking the tuna.
Drizzle each tuna steak with olive oil and season with salt and pepper on all sides. pour sesame seeds on a plate, and coat each steak by laying each seasoned side against seeds. Set aside on a cookie sheet.
Melt butter in a flat bottomed pan over medium high heat. When butter is foaming, place a steak in the pan. Allow to sear for 2 minutes, then flip to the other side. Allow to cook for another 2 minutes. Repeat with other steak. Allow the cooked tuna to rest for a few minutes before slicing into ¼ inch thick slices.
Plate a layer of the salad, then splay sliced tuna steak across the top. Sprinkle with leftover sesame seeds.