Prepare ingredients: Chop the carrot and potato into half-inch and two-thirds inch cubes. Dice the zucchini, slice the onion and garlic, and cut the chicken breast into one-inch cubes.
Cook chicken: Heat a pot on medium-high, add oil, and cook the chicken thighs skin-side down for 1 minute, then reduce heat to medium-low.
Add aromatics and sauce: Mix in gochujang, gochugaru, onion, garlic, tomato paste, ginger, garlic paste, dark soy sauce, oyster sauce, rice vinegar, and black pepper. Toss gently and cook for 3-4 minutes, stirring every 15 seconds.
Simmer: Add 1 cup of water, potatoes, and carrots; simmer with lid closed for 15 minutes. Then, add zucchini and bell pepper, simmer for another 10 minutes. If needed, adjust water and cook for 5 more minutes. Pair with steamed rice and banchan, and enjoy!