Pat the fish dry and season lightly with a pinch of salt and pepper.
Warm the olive oil in a Dutch oven over medium heat.
Sauté onion and bell pepper until softened, about 5 minutes.
Stir in garlic, paprika, and red pepper flakes; cook until fragrant, 30 seconds.
Pour in the wine and simmer until reduced by half, about 2 minutes.
Add crushed tomatoes and stock. Bring to a gentle boil, then season with remaining salt and black pepper.
Lower heat and simmer uncovered for 10 minutes to meld flavors.
Nestle the fish into the stew. Simmer gently until just cooked and flaky, 6–8 minutes.
Finish with lemon juice and parsley. Taste and adjust seasoning, then serve hot.