Heat oven to 425°F and line a large baking sheet.
Toss carrots, potatoes, bell pepper, and onion with 1.5 tbsp oil, 0.5 tsp salt, and the paprika. Roast 20–25 minutes, stirring once, until edges brown.
Pat chicken dry. Season with 0.5 tsp salt and 0.25 tsp pepper. Dust evenly with the flour.
Warm remaining 1.5 tbsp oil in a Dutch oven over medium-high. Brown chicken in two batches, 4–5 minutes total. Transfer to a plate.
Add celery to the pot and cook 2 minutes. Stir in garlic and tomato paste; cook 1 minute until the paste darkens.
Pour in 1 cup broth to deglaze, scraping up browned bits.
Return chicken to the pot. Add remaining broth, diced tomatoes, thyme, rosemary, and the remaining pepper. Bring to a boil, then reduce to a gentle simmer. Cover and cook 20 minutes.
Stir in the roasted vegetables. Simmer uncovered 8–10 minutes, until potatoes are tender and the stew thickens slightly. Adjust salt to taste.
Finish with lemon juice and parsley. Let rest 5 minutes before serving.