Rinse rice in cold water until water runs clear (3-5 rinses). Combine rice, water, and kombu in a pot and let soak for 30 minutes. This soaking ensures even cooking and perfect texture.

Bring rice to a boil over high heat. Once boiling, remove kombu, reduce heat to low, cover, and simmer for 15 minutes. Remove from heat and let steam, covered, for 10 minutes without peeking.

While rice steams, mix vinegar, sugar, and salt in a small saucepan. Heat gently until sugar dissolves, then cool. Transfer hot rice to a large shallow dish and drizzle with vinegar mixture while using cutting motions with your paddle. Fan the rice as you mix for that glossy restaurant finish.

Cut cucumber into long matchsticks about 1/4-inch thick and pat dry. Slice avocado into 1/2-inch strips just before rolling. For Hawaiian style, slice spam into 1/4-inch strips and pan-fry over medium-high heat until edges are crispy, about 3-4 minutes per side.

Place bamboo mat on work surface with slats running horizontally. Position nori sheet shiny-side down on the mat. Prepare tezu water by mixing water with a splash of rice vinegar in a small bowl.

Dip hands in tezu water to prevent sticking. Spread 3/4 cup rice evenly over nori, leaving a 1-inch border at the far edge. Rice layer should be about 1/4-inch thick - you should see nori peeking through. Create a shallow groove horizontally across the rice, 1 inch from the bottom edge.

Arrange fillings in the groove without overfilling. Lift the mat edge closest to you with thumbs while holding fillings in place with other fingers. Roll forward in one confident motion until the mat touches rice on the far side. Gently squeeze to compress, then complete rolling.

Use a sharp knife wiped with a damp towel between cuts. Cut each roll into 6-8 pieces. Sprinkle with sesame seeds and serve immediately with soy sauce, wasabi, and pickled ginger.