In a small bowl, whisk together the sesame oil, coconut aminos, grated fresh ginger, and the juice from the half lime to create the dressing.
Thinly slice the cucumber and radishes, and trim the ends of the snap peas.
In a large bowl, toss the mixed baby greens, snap peas, cucumber, and radishes with half of the prepared dressing.
Pat the tuna steak dry with a paper towel and season both sides with sea salt and black pepper.
Heat the avocado oil in a cast-iron skillet over medium-high heat until just shimmering.
Sear the tuna for 1 to 2 minutes per side for medium-rare, ensuring a golden-brown crust forms.
Remove the tuna from the pan and let it rest for 2 minutes before slicing into 1/2-inch thick pieces.
Plate the salad greens and top with the sliced tuna, then drizzle with the remaining dressing and garnish with sesame seeds.