I made Tuna Cutlet Rice bowl with the same ingredients and it was so good and I wanted to make for my husband. Since he is not a rice person, I made sandwiches with these ingredients. He loved it so much!
Sprinkle salt and black pepper over each tuna and set aside for 10 minutes. Then spread mayonnaise over each tuna, coat with panko, put on a plate, cover with plastic wrap and refrigerate for 30 minutes.
Make sauce. In a shallow medium bowl or plate, mix together peanut butter, soy sauce and gochujang. Set aside.
Make namuru. Slice shiitake mushrooms and chop scallions. In a fry pan, heat sesame oil and cook carrots over medium heat until tender. Add scallions and shiitake mushrooms and sauté until tender. Stir in garlic. Then add salt and toss to coat. Remove from the heat and set aside.
After 30 minutes, take tunas out of the refrigerator. In a fry pan, heat enough canola oil to deep-fry tunas over medium-high heat and deep-fry all sides of tunas until golden brown. Drain on paper towels then put into the sauce bowl or plate. Coat all sides of each tuna cutlet with the sauce.
On bottom of sandwich bun, put lettuce leaves and one tuna cutlet. Put the namuru on top and top of the bun to close sandwich. Make one more sandwich.