Preheat the oven to 425°F. Line a large rimmed sheet pan with parchment paper or lightly grease it.
Place the halved baby potatoes in a large bowl.
Add 2 tablespoons olive oil, garlic powder, onion powder, paprika, Italian seasoning, ½ teaspoon salt, and ¼ teaspoon black pepper.
Toss until the potatoes are evenly coated with the oil and seasonings.
Arrange the potatoes cut-side down on the prepared sheet pan, leaving space between them.
Roast the potatoes for 20 minutes.
While the potatoes roast, pat the chicken thighs dry with paper towels.
Rub the chicken with the remaining 1 tablespoon olive oil. Season with the remaining ½ teaspoon salt, ¼ teaspoon black pepper, thyme, and red pepper flakes if using.
Remove the sheet pan from the oven and turn the potatoes.
Nestle the chicken thighs among the potatoes with the skin facing up.
Return the sheet pan to the oven and roast for 25 to 30 minutes. The chicken should reach at least 165°F internally, and the potatoes should be tender.
For additional browning, broil for 1 to 2 minutes. Watch closely so the chicken skin doesn't burn.
Remove the pan from the oven and let the chicken rest for 5 minutes.
Sprinkle the chicken and potatoes with fresh parsley and serve warm.