Heat the oil in a large, deep pan over medium heat.
Add the onions and sauté until soft and golden.
Add the garlic and cook for 1 minute until fragrant.
Stir in the tomatoes, tomato paste, sugar, paprika, salt, and pepper. Cook 5–7 minutes until the sauce thickens slightly.
Pour in the fish stock (or water) and bring to a gentle simmer.
Carefully place the snoek pieces in the sauce, skin-side up. Spoon some sauce over the fish.
Cover and simmer gently for 20–25 minutes, basting occasionally, until the fish is cooked through and tender.
Taste and adjust seasoning. Add a splash of vinegar if desired.
Garnish with chopped parsley and serve hot.