Strain the canned tuna through a fine sieve, pressing with a fork to remove excess liquid. Discard the liquid, then combine the tuna, green onion, Kewpie mayo, and sriracha sauce in a medium bowl. Mix well and set aside.
In a large bowl, season the hot cooked rice with sesame oil, sesame seeds, and salt. Mix well, then cover with a damp towel or lid to keep the rice warm and prevent it from drying out.
Place a sheet of gim or nori vertically on a cutting board or bamboo sushi mat, rough side facing up. Place half of the seasoned rice in the center and spread it evenly with clean, wet hands or a rice paddle, leaving a 1-inch border along the far edge.
Place two perilla leaves in the center of the rice, overlapping them so they fit within the seaweed sheet. Add half of the spicy tuna mixture and shape it into a thick log rather than spreading it thinly. Fold the perilla leaves over the tuna to help contain the filling.
Starting from the edge closest to you, firmly roll and tuck the ingredients together without squeezing out the tuna filling. Finish rolling toward the exposed 1-inch border, then place the kimbap seam-side down.
Drizzle ½ teaspoon sesame oil over the kimbap and spread it evenly over the seaweed with clean hands or a brush. Lightly coat a sharp knife with sesame oil. Gently hold the roll in place and slice it into 1-inch pieces. Garnish with sesame seeds. Repeat with the remaining ingredients to make the second roll. Serve immediately.