Cook your two cups of rice. Add those 2 cups into a large bowl. Add 1 tbsp sesame oil and 1/2 tsp salt to cooked rice. Combine with a rice paddle if one is available. In another bowl, combine tuna, soy sauce and mayonnaise.
Place a piece of plastic wrap over a small bowl and fill with rice. Remove plastic from bowl and twist into a ball. Next, you'll want to flatten the rice ball on a flat surface. Add about a tablespoon of filling to the center of the flattened rice ball. Gather all edges of the plastic wrap together and twist to form into a ball again. Repeat this process four more times. Optional: roll rice balls in dish filled with black sesame seeds.
Set pan to medium heat. Once pan is hot, add in a few tablespoons of sesame oil. Add rice balls to pan and sear for at least 5 minutes on each side to get a nice, crispy outer texture. Add a few more minutes if you'd like rice balls to be a bit more golden. Serve over a salad or with your favorite veggies.