While rice is cooking, cut the cucumber into approximately 3 inch long sticks.
1/2 English cucumber
Cut the carrots to approximately 3 inch long matchstick size.
Cut the avocado into sticks-ish. Avocado slices are awkward shaped, so just cut them into skinny-ish pieces.
Combine the tuna with the soy sauce, mirin, and sugar, breaking into small pieces.
1 5oz can albacore tuna, 1 T soy sauce, 1 T mirin, 1 T sugar
Cook in a small sauce pan over medium heat.
Let the mixture simmer until the tuna has soaked in the sauce and the pan is mostly dry.
Set aside in a bowl.
Whisk eggs together with a pinch of salt, and pour about 1/3 of it into a small non-stick pan, preferably a square tamagoyaki pan, but whatever you have on hand should work, as long as it's not too big.
When the bottom is cooked and the top is starting to look cooked through, start rolling the egg up.
When the egg is all on the other side, pour another 1/3 of it in and repeat, rolling back.
Put the remaining 1/3 in, and roll it up. Now you should have a nice rolled egg.If you don't want to do that, then scramble the eggs. It won't look as nice but it should technically work.
If you made the rolled egg, cut into sticks about the size of the cucumber sticks.
Cut your seaweed sheets in half.
10 sheets sushi nori (seaweed)
When the rice is done, transfer it to a large bowl, and pour the vinegar mix over it.
Quickly, using your rice scooper or a thin spatula, stir the mixture until fully combined with rice. You want to use a sort of "cutting" motion, so you don't smash the rice up.