Place the diced chicken in a medium bowl and season with 1 teaspoon salt, onion powder, garlic powder, 1/2 teaspoon black pepper, and 1/2 teaspoon dried thyme; toss to coat evenly.
Heat a large skillet over medium heat and melt 3 tablespoons of the butter. Add the seasoned chicken and cook, stirring occasionally, until cooked through and registers 165°F on an instant-read thermometer, about 6–8 minutes. Remove the chicken to a plate and set aside.
Add 1 tablespoon butter to the skillet, then add the diced onion and red bell pepper; cook 1–2 minutes until they begin to brown. Add the garlic and cook 1 more minute until fragrant.
Pour the 2 cups low-sodium chicken stock into the pan and bring to a boil. Add the broccoli florets, cover, and cook 2 minutes to steam.
Remove the lid and push the vegetables to the sides of the skillet. Let the stock simmer until reduced by about half, roughly 5 minutes.
Stir in the remaining 1 tablespoon butter, return the cooked chicken and any juices to the skillet, and toss to coat and rewarm. Taste and adjust with additional salt and pepper as desired, then serve hot.
