Pat the ahi tuna dry with paper towels. Trim any sinew. Cut the steak into 12 bite-sized cubes or 24 smaller pieces (about 3/4–1 inch each) so they cook quickly and evenly.

Make spice rub

In a small bowl combine kosher salt, black pepper, smoked paprika, garlic powder, onion powder, ground cumin and cayenne. Stir to evenly distribute.

Season tuna

Lightly rub the spice mix over all sides of the tuna cubes so each piece is evenly coated. Let rest at room temperature for 5–10 minutes to allow flavors to adhere.

Sear

Heat a large heavy skillet or cast-iron pan over high heat until very hot (2–3 minutes). Add the neutral oil and swirl to coat. Working in a single layer (do not crowd; do in batches if needed), place tuna bites in the pan and sear for 20–30 seconds per side for rare (pink center). For medium-rare sear ~45 seconds per side; avoid overcooking. Use tongs or a spatula to rotate pieces so all sides get a quick sear to blacken the spices. Total cook per batch should be about 1–2 minutes.

Rest

Transfer seared tuna bites to a plate and let rest 1–2 minutes before assembling to keep juices even.

Wasabi Aioli

In a small bowl whisk together mayonnaise and creme fraiche until smooth. Add wasabi paste, lemon juice, soy sauce, honey, toasted sesame oil, salt and pepper. Taste and adjust heat or acidity: add more wasabi for spice, more lemon for brightness. Refrigerate until ready to serve (can be made up to 24 hours ahead).

To Serve / Garnish

Arrange warm tuna bites on a platter or individual plates. Spoon or pipe small dollops of wasabi aioli alongside or place a shallow pool in the center for dipping.

Sprinkle with toasted sesame seeds and scatter microgreens or sliced scallions over the bites. Serve with lime or lemon wedges for an optional squeeze of citrus.

Serve immediately so the tuna remains warm with a rare center and the aioli provides cool sharpness.