Rinse the sushi rice until the water runs mostly clear.
Cook the rice according to package instructions, then let it sit covered for 10 minutes.
In a small bowl, warm the rice vinegar, sugar, and salt together until fully dissolved.
Pour the vinegar mixture over the hot rice and gently mix until evenly coated. Allow the rice to cool to room temperature.
Lightly spray an ice cube tray with avocado oil or another neutral oil.
Line the tray with plastic wrap.
Add smoked salmon and avocado slices into each compartment.
Add cucumber slices on top of the salmon and avocado.
Pack the sushi rice tightly into each compartment, pressing down firmly.
Flip the tray onto a cutting board and carefully remove the tray and plastic wrap.
Drizzle with spicy mayo and unagi sauce or teriyaki sauce.
Top with chopped green onions and fried onions if desired.
Serve immediately and enjoy.