Pat the chicken thighs dry with paper towels and place them in a bowl. Add 1.5 tbsp olive oil, smoked paprika, Italian seasoning, onion powder, 0.5 tsp salt, and 0.25 tsp black pepper. Toss to coat and let marinate while you prep the vegetables.

In a large bowl, combine baby potatoes, carrots, and onion. Add the remaining 1.5 tbsp olive oil, remaining 0.5 tsp salt, remaining 0.25 tsp black pepper, and minced garlic. Toss until the vegetables are evenly coated.

Preheat a large, deep skillet over medium high heat. Add the marinated chicken thighs in a single layer and cook for 3 minutes per side until lightly golden on the edges. Transfer the chicken to a plate, leaving any browned bits in the skillet.

Add the potato, carrot, and onion mixture to the hot skillet, spreading it into an even layer. Cook undisturbed for 4 minutes, then stir and cook for 4 more minutes until the vegetables start to brown on the edges.

Stir in the sliced red bell pepper and cook for 2 minutes, tossing occasionally, until the pepper begins to soften.

In a small bowl, whisk together the chicken broth, lemon juice, and Dijon mustard. Pour the mixture into the skillet and scrape up any browned bits from the bottom of the pan.

Nestle the browned chicken thighs on top of the vegetables, along with any juices from the plate. Reduce the heat to medium low, cover the skillet, and simmer for 12 minutes.

Remove the lid and continue to cook for 5 to 7 minutes until the sauce slightly thickens, the vegetables are tender, and the chicken reaches 165°F in the center with caramelized edges.

Turn off the heat and stir the butter into the sauce until melted. Let the pan rest for 3 minutes, then sprinkle with chopped fresh parsley and serve straight from the skillet.