Cook your rice depending on the directions in the manual of your rice cooker or by cooking it on the stove.
While the rice is cooking, slice the tuna and avocado. Once rice is done, add rice vinegar and sugar and mix.
Lay a sheet of sushi nori on the sushi mat.
Spread the rice evenly on sushi nori sheet. Do not add too much rice, you want enough rice to just cover the sushi nori.
Add 2 or 3 slices of tuna on top of the rice near one end of the sheet. You want to leave a little bit of open space at the end.
Add 2 or 3 slices of avocado, about ½ tablespoon of spicy mayo, and a sprinkle of sesame seeds.
Fold the end of the sheet closest to the fillings over the fillings. Slightly tuck under using the sushi mat.
Continue to roll the sheet using the sushi mat until a tight roll is formed.
Slice roll using a filet knife into about 1 inch slices. Sprinkle with sesame seeds and drizzle spicy mayo if desired.
Serve with a side of spicy mayo or soy sauce.