Pat the chicken thighs dry and season both sides with salt and pepper.
Heat 1 tablespoon olive oil in a large skillet over medium-high heat.
Add the chicken to the hot skillet and cook 4–5 minutes per side until an instant-read thermometer registers 165°F (74°C). Remove the chicken and set aside.
In the same skillet, whisk together 1/2 cup brown sugar, 1/3 cup low-sodium soy sauce, 2 tablespoons hoisin sauce, 1 tablespoon sweet chili sauce, 1 tablespoon grated ginger, 1 teaspoon minced garlic, and the juice of 1 lime; add red pepper flakes to taste.
Bring the sauce to a boil over medium heat, then reduce to low and simmer until it thickens slightly, about 2–4 minutes.
Return the chicken to the skillet and coat both sides with the sauce. Simmer briefly until the sauce is sticky and clings to the chicken, about 1–2 minutes more.
Remove from heat and transfer to a serving plate; garnish as desired (sesame seeds and chopped green onions are optional).