In a large bowl, whisk together the gochujang, soy sauce, ginger, and oil.
Add chicken thighs and vegetables and toss to coat evenly. Let sit for 30 minutes at room temperature, or cover and refrigerate for up to overnight.
Preheat your oven to 425°F (220°C).
Nestle the marinated chicken thighs, skin-side up, among the vegetables on a parchment paper lined sheet pan.
Roast everything for 35–45 minutes, or until:
Chicken skin is browned and crisp or internal temperature of chicken reaches 165°F and vegetables are tender and slightly caramelized. Optional: Broil for 1–2 minutes to crisp the skin further.
While the chicken roasts, toss the radishes and scallion greens with the rice vinegar and sesame oil. Let sit at room temperature to lightly pickle.
Top the roasted chicken and vegetables with the pickled radish/scallion mixture. Serve with steamed rice and lime wedges, if desired.