Method
Make the cucumber side
Slice the cucumber into rounds approximately ⅛ inch thick. Stir together rice vinegar, sesame oil, sugar or maple syrup, and salt. Toss with the cucumber and let rest for 10–15 minutes, covered or refrigerated.
Prepare the tuna
Combine the tuna's tamari, sesame oil, ginger, garlic, and honey or maple syrup. Pat the steaks dry, brush with the marinade, and let sit for 5–10 minutes. Press both flat sides into sesame seeds and season lightly with black pepper.
Stir-fry the vegetables
Heat 1 tbsp avocado oil in a large skillet or wok over medium-high heat. Add mushrooms in a single layer, leave undisturbed for 2 minutes, then stir and cook until lightly browned, about 3–4 minutes total. Add carrots and bok choy stems. Stir-fry for 2–3 minutes. Add garlic and ginger and stir for 30 seconds. Mix the vegetable sauce: tamari, sesame oil, rice vinegar, and honey or maple syrup. Add the bok choy leaves and sauce. Toss for 1–2 minutes until the leaves wilt. Season to taste and transfer to serving bowls.
Sear the tuna
Wipe out the skillet and heat over medium-high to high heat. Add 1 tbsp avocado oil. When shimmering, carefully add the tuna. The original recipe used 45–60 seconds per side for a rare center, 60–90 seconds for medium-rare, or 2–3 minutes for medium, based on 1-inch steaks. These times are approximate and do not establish a safe internal temperature. Food safety: Cook fish to 145°F internally for the fully cooked option. Rare or medium-rare tuna carries additional foodborne illness risk.
Rest, slice, and assemble
Rest the tuna for 2 minutes, then slice against the grain into ½-inch strips. Arrange over the hot vegetables. Add the cold cucumber alongside and finish with optional sesame seeds and scallions.