If using chicken breasts, pound them to 1⁄2-inch thickness so they cook quickly and tenderize fully. Cut chicken into bite-sized pieces. Place in a bowl or plastic bag.
In a small bowl, whisk together the gochujang, soy sauce, sesame oil, garlic, brown sugar, rice vinegar, and ginger. Pour over the chicken. Toss to coat.
Cover and marinate for at least 30 minutes, up to overnight.
Cook using one of the following methods:
Pan-fry: Heat 1 Tbsp oil in a skillet over medium-high heat. Add chicken and cook 5-8 minutes per side until browned and cooked through. Toss with sauce from marinade bowl to coat.
Bake: Place chicken on a parchment-lined baking sheet. Bake at 400°F for 25-30 minutes until cooked through and caramelized on edges. Toss with sauce to coat.
Grill: Grill chicken over medium heat for 6-10 minutes per side depending on thickness. During last 2 minutes, brush with reserved marinade sauce to glaze.
Air Fry: Cook battered chicken at 400°F for 8-12 minutes, flipping halfway, until cooked through and crispy. Toss in sauce to coat.
Instant Pot: Combine chicken and marinade in pot. Cook at high pressure for 5-8 minutes then quick or natural release. Shred chicken and toss with sauce.
Slow Cooker: Place chicken and marinade in cooker. Cook on low for 4 hours or high for 3 hours until chicken is very tender.
Garnish with sesame seeds and green onions if desired. Enjoy with rice and vegetables.