Wash the fish, dab dry and cut into large cubes. Sprinkle with lemon juice. Leave to stand for about 10 minutes. Wash arugula and tomatoes. Halve the tomatoes. Pluck the rocket into bite-sized pieces.
Cut onion into fine slices. Peel and chop garlic. Dab fish dry if necessary. Heat 1-2 tablespoons of oil. Fry the fish for 3-4 minutes until golden brown all around. Remove and season with salt and pepper. Fry onion and garlic in hot frying fat until transparent. Add the tomatoes and rocket and fry briefly. Drizzle with vinegar. Season with salt and pepper. Arrange fish cubes and vegetables on a plate.
Remove and season with salt and pepper. Fry onion and garlic in hot frying fat until transparent. Add the tomatoes and rocket and fry briefly. Drizzle with vinegar. Season with salt and pepper. Arrange fish cubes and vegetables on a plate. Garnish with lemon wedges if desired. Serve with baguette