Cut the chicken breast into bite-sized cubes and set aside.
In a small bowl, whisk together the gochujang, tamari, sesame oil, honey, minced ginger, minced garlic, red pepper flakes, and water until smooth.
Heat a medium oven-safe skillet over medium-high heat.
Add the chicken to the skillet and cook for 5-6 minutes, stirring occasionally, until the chicken is browned and cooked through.
Pour the sauce mixture over the chicken and stir well to coat every piece.
Simmer the sauce for 2 minutes until it thickens into a glossy glaze that clings to the meat.
Turn off the heat and spread the chicken into an even layer in the skillet.
Sprinkle the shredded mozzarella cheese evenly over the top of the chicken.
Place the skillet under the broiler for 2-3 minutes until the cheese is melted, bubbly, and has golden-brown spots.
Garnish with thinly sliced green onions and sesame seeds before serving.