Cook the rice: Rinse sushi rice until the water runs mostly clear. Add to a pot with water, bring to a simmer, cover, and cook on low for 15 minutes. Rest off heat for 10 minutes.

Season the rice: Warm rice vinegar, sugar, and salt until dissolved. Gently fold into the hot rice in a wide bowl. Fan or let cool to room temperature, keeping it covered with a damp towel so it doesn’t dry out.

Prep fillings: Cut cucumber into thin matchsticks and slice avocado. Pat shrimp dry. If using vegetables, slice into thin, uniform pieces so they cook quickly.

Heat the oil: Fill a deep pan with 1 1/2–2 inches of oil. Heat to 350–360°F (175–182°C). Keep the temperature steady for crisp, non-greasy tempura.

Make the tempura batter: Whisk flour, cornstarch, baking powder, and salt. Add ice-cold sparkling water gradually until the batter is thin and lumpy, like melted ice cream. Do not overmix.

Fry the tempura: Lightly dust shrimp or veggies with flour. Dip in batter and fry in small batches 2–3 minutes until pale golden and crisp. Drain on a rack. Tip: Keep pieces small so rolls aren’t overstuffed.

Set up your rolling station: Lay a sheet of nori, shiny side down, on the mat. Wet your fingers and spread a thin, even layer of rice over the nori, leaving a 1-inch border at the top.

Add fillings: Place 2–3 pieces of tempura along the center. Add a few cucumber sticks and avocado slices. Drizzle a small line of spicy mayo or eel sauce if you like.

Roll it up: Lift the edge of the mat closest to you and fold it over the fillings, tucking tightly to shape a cylinder. Press gently to seal, then continue rolling until the end. Wet the top border of the nori to help it stick.

Slice cleanly: Dip a sharp knife in water and slice the roll into 6–8 pieces, wiping the blade between cuts. Garnish with sesame seeds and more sauce if desired.

Serve: Plate with soy sauce, pickled ginger, and wasabi. Enjoy while the tempura is still crisp.