Preheat the oven to 425°F (218°C). Line a baking sheet with parchment paper or lightly oil it.
In a medium bowl, whisk together 1/2 cup ketchup, 2/3 cup honey, minced garlic, 1/4 cup soy sauce, 1 Tbsp melted butter, 1/2 tsp cracked black pepper, 1/2 tsp sea salt and 1/4 tsp crushed red pepper (if using) until smooth.
Add the chicken thighs to the sauce and toss to coat evenly; let them sit while you prepare the peppers.
Remove stems and seeds from the red and green bell peppers and slice them thinly.
Place the coated chicken thighs on the prepared baking sheet, leaving space between pieces. Toss the sliced peppers quickly in any remaining sauce and spread them evenly around the chicken. If there is extra sauce, brush or spoon it over the chicken.
Bake for about 25–30 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
When you remove the pan from the oven, carefully drain any excess liquid if desired, then let the chicken rest for about 5 minutes before serving.
Serve the chicken and peppers over rice if desired and sprinkle with sesame seeds for garnish.