Drain the oil from the tuna using a strainer.
Finely chop onion, green onion, and Cheongyang chili pepper.
In a mixing bowl, combine tuna, doenjang (soybean paste), gochujang (red chili paste), and the chopped vegetables.
Add minced garlic, sesame oil, and toasted sesame seeds; mix well.
Serve the finished ssamjang with cucumber, perilla leaves, or other vegetables.