Place your cutting board and chef's knife in the freezer for 10 minutes to chill.

Inspect the sashimi-grade tuna for freshness, then pat dry and keep refrigerated until ready to cut.

Using the chilled knife, dice the tuna into 1/4-inch cubes in one clean motion per cut, wiping the blade between slices.

In a small mixing bowl whisk together olive oil, lemon juice, lime juice, soy sauce, and sesame oil to form a light dressing (about 30 seconds).

Add diced tuna, minced shallot, and optional sriracha to the bowl and fold gently 10–15 times until every cube is lightly coated.

Season with kosher salt and black pepper a pinch at a time, tasting after each addition until balanced.

Cover and refrigerate the tartare for 5–10 minutes to let flavors meld while you chill serving plates.

Portion the tartare onto chilled plates with an ice cream scoop, then garnish with toasted sesame seeds, chopped chives, and microgreens immediately before serving.