Season fish pieces with salt and pepper and dredge them in flour.
Heat oil in a deep skillet and fry fish in batches until done and browned on all sides. Remove from the skillet and drain in paper towel. Set aside.
Heat more oil in the skillet and sauté onions and garlic for 1 – 2 minutes; add tomatoes and cook, stirring for 2 minutes more. Stir in ají and chopped parsley and mix. Sauté for 2 minutes and add soy sauce and vinegar (add soy sauce and vinegar, 1 tablespoon at a time and then taste; add more if desired). Season to taste with salt and pepper. Stir in fish pieces and mix. Add lemon juice, gradually and mix.
Serve with white rice and french fries.
Other ways to prepare fish:
Cod Casserole from Liguria
Halibut with red pepper sauce
Fish fillets in brown sauce with capers