Spread sesame seeds on a plate and press the top and sides of the tuna into the seeds so they adhere, leaving the very center of each long face mostly plain (this gives a thin sesame crust while preserving a rare center).

Sear

Heat a heavy skillet (cast-iron or stainless) over high heat until very hot, about 2–3 minutes. Add 1 tablespoon neutral oil and swirl. Add the tuna and sear 30–45 seconds per side for rare (adjust 60–75 seconds per side for medium-rare), turning with tongs so all edges get a quick sear. If using, add 1/2 tablespoon butter to the pan in the final 15 seconds and spoon melted butter over the tuna for gloss. Remove tuna to a cutting board and let rest 2–3 minutes before slicing thinly across the grain into 1/4-inch slices.

Dressing

In a small bowl or jar combine 2 tablespoons low-sodium soy sauce, 1 tablespoon rice wine vinegar, 1 tablespoon fresh lime juice, 1 teaspoon toasted sesame oil, 1 teaspoon honey (or agave), 1/2 teaspoon grated fresh ginger, 1/2 teaspoon minced garlic and 1 tablespoon neutral oil. Whisk or shake vigorously until emulsified. Taste and adjust—add a pinch of salt if needed or 1/4 teaspoon crushed red pepper flakes for heat.

Salad Base

Assemble the salad: divide 4 cups mixed salad greens between two plates or bowls. Arrange half the sliced cucumber, half the radishes, half the avocado slices and half the sliced scallions on each plate. Drizzle a small amount (about 1 tablespoon) of dressing over each salad and gently toss or turn the ingredients to coat—reserve most dressing for finishing after plating.

Garnish & Serve

Place sliced seared tuna across each salad. Drizzle remaining dressing over the tuna and salad. Finish with a light drizzle (about 1/8–1/4 tsp) of sesame oil if using, sprinkle toasted sesame seeds, add 1 tablespoon pickled ginger per plate if desired, and serve with lime wedges alongside.

Serve immediately while tuna is warm. Leftovers: store tuna slices and salad components separately; consume tuna within 24 hours.