Preheat the oven to 400°F (207°C).
Rinse the chicken thighs under cold water and pat dry with paper towels. Season both sides with salt, ground black pepper, and smoked paprika. Place the chicken in a large bowl and toss with lemon juice and chopped parsley.
Heat 1 tablespoon olive oil in a skillet over medium-high heat. Sear the chicken thighs 2–3 minutes per side until nicely browned but not fully cooked. Remove the chicken and set aside.
Add the remaining 1 tablespoon olive oil to the skillet and reduce heat to medium. Sauté the minced garlic and sliced red onion until the onion is slightly softened, about 2–3 minutes.
Add the halved baby potatoes, 1/4 teaspoon salt (or to taste), and brown sugar to the skillet. Stir to combine and coat the potatoes with the onion and garlic mixture.
Return the seared chicken along with any accumulated juices to the skillet, arranging the thighs among the potatoes and onions.
Transfer the skillet to the lower third of the preheated oven and bake for 30–40 minutes, until the potatoes are tender and the chicken is cooked through.
If the chicken surface becomes too dark while baking, loosely cover with aluminum foil. Serve immediately.
