Wash rice, drain and put it in a medium pot. Add water and let it sit for 30 minutes. After 30 minutes, bring to boil with lid.
Once boiled, simmer on low heat. Cook for 10 minutes until done. (Do not remove the lid while cooking). Remove from heat and let it sit for 10 minutes. Mix lightly with spoon to serve.
In the mean time, add red onions and cucumbers into a small bowl. Sprinkle ⅓ tsp of salt and let it sit for 10 minutes. Take them out onto a paper towel and squeeze to remove water.
Drain water from canned tuna and add it in a small bowl with cucumbers and onions. Mix in jalapeño, mayonnaise, salt, and pepper.
Wet hands (this will keep your hands from sticking to rice). Sprinkle some salt on your hands to add little flavor to the rice.
* You can do this using plastic wraps or gloves if you don't want to use your hands.
Take 1 serving of rice in your hand. Make a small hole in the middle and insert tuna salad mixture inside. Cover the hole with rice. Shape it into triangle (or round shape, if you like).
Once you are done making the shape, wrap it with nori seaweed.