Pat the sushi-grade white tuna dry with paper towels. Using a very sharp knife, trim any sinew and cut the tuna into very thin slices (about 1/8" thick). Arrange slices in a single layer on a chilled serving plate or platter.

Prepare jalapeño

Thinly slice the jalapeño crosswise into rounds (about 1–2 mm thick). For less heat, remove the seeds and membranes from half of the jalapeño before slicing. Reserve 2 extra slices for garnish.

Make the ponzu-lime dressing

In a small bowl whisk together the ponzu sauce (3 tbs), fresh lime juice (1 tbs), light soy sauce (1 tsp), sesame oil (1 tsp) and mirin (1 tsp, optional). Taste and adjust balance — it should be bright, tangy, slightly salty with a hint of sweetness.

Spoon or lightly drizzle about 1 tablespoon of the ponzu-lime dressing evenly over the arranged tuna slices so each slice gets a thin coating. Allow tuna to sit for 1–2 minutes to slightly 'marinate.'

Assembly & Garnish

Top the dressed tuna with the thin jalapeño rounds, distributing them so most slices have at least one jalapeño piece. If you removed seeds earlier, place a few seeded rings where you want more heat.

Sprinkle the toasted sesame seeds evenly over the tuna and jalapeño. Scatter the microgreens or thinly sliced green onion over the top for color and freshness.

Lightly drizzle the neutral oil (or EVOO) in a very thin stream around the plate (not over the tuna) or as a hairline over the fish for sheen. Finish with a small pinch of sea salt or flaked salt across the fish to taste.

Garnish with the reserved jalapeño slices. If desired, serve immediately with cucumber rounds or toasted baguette slices on the side so guests can top and eat, or serve the tuna directly on the platter as a shared appetizer.

Notes & Timing

Serve immediately after assembling. Total standing time after dressing should be 1–3 minutes; do not let raw fish sit in citrus-based marinades for long to preserve texture. Adjust jalapeño quantity to taste.