Preheat the oven. Preheat oven to 425°F. Line a large sheet pan with parchment paper or lightly coat it with cooking spray for easier cleanup.
Prepare the lemon herb marinade. In a large mixing bowl, whisk together olive oil, lemon juice, zest, dijon mustard, garlic, rosemary, thyme, paprika, salt and pepper. Mix until everything is well combined.
Season the potatoes. Add the potatoes to the bowl and toss them with half of the marinade until evenly coated. Arrange the potatoes cut-side down on the prepared sheet pan in a single layer.
Roast the potatoes. Roast the potatoes for 20 minutes. This head start helps them become golden and tender while ensuring they finish cooking at the same time as the chicken.
Marinate the chicken. While the potatoes are roasting, add the chicken thighs to the remaining lemon herb sauce in the bowl. Toss well to coat and allow them to marinate in all those wonderful flavors while the potatoes cook.
Add the chicken. Remove the sheet pan from the oven and carefully flip the potatoes. Arrange the marinated chicken thighs skin side up around the potatoes and sprinkle everything with a little extra salt and pepper, if desired.
Finish roasting. Return the pan to the oven and bake for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the potatoes are tender. For extra crispiness and golden brown color, switch the oven to broil for the final 2 to 3 minutes.
Serve and enjoy. Let everything rest on the pan for a few minutes before serving. Garnish with fresh rosemary, thyme, lemon slices, or chopped parsley, if desired.