Preheat the oven to 375°F (190°C), or 170°C if using a fan oven.
Pat the chicken thighs dry with paper towels. Season both sides with salt and pepper.
Heat olive oil in a large oven-safe skillet over medium-high heat. Place the chicken thighs skin-side down and sear for 2-3 minutes, until the skin is golden and crispy. Remove the chicken from the skillet and set aside (The chicken will not be fully cooked at this stage).
Drain excess fat from the skillet, leaving about 1 tablespoon. Add the diced onion and cook until softened and translucent, about 1-2 minutes.
Stir in the couscous and toast it for 1 minute, stirring frequently. Add smoked paprika and garlic, cooking for 30 seconds until fragrant.
Pour in the chicken stock and lemon juice. Stir to combine, then nestle the chicken thighs skin-side up into the couscous mixture.
Cover the skillet with a lid or foil and transfer to the preheated oven. Bake for 15 minutes covered, then remove the lid and bake for an additional 5-10 minutes until the chicken is cooked through and the couscous is tender and fluffy.
Remove from the oven and garnish with fresh chopped parsley. Drizzle with extra lemon juice if desired.