Cut the carrots into thick rounds, the potatoes and onion into big chunks, and the scallions into two-inch pieces, then set them to the side.
For the sauce, combine the gochujang, light soy sauce, mirin, gochugaru, sugar, and sesame oil, and mix until everything is well incorporated.
Add the sauce to a pot along with the water and bring it up to a simmer.
Add the potatoes, carrots, and onions, and let them cook in the broth for a few minutes.
Add the chicken thighs, cover the pot, and let everything braise until the potatoes are tender and the chicken is cooked through, about 20 to 25 minutes.
Add the scallions and give everything one last stir while the sauce reduces slightly.
Spoon the braise into a bowl. Optionally garnish with sesame seeds. But it's your food, you eat it how you like.