Crush or finely chop the garlic. Finely chop the onion and tomato. Coarsely chop the potatoes, celery and carrot. Finely chop the parsley, including the stems. Finely grate the lemon zest, then juice. Crumble 1 stock cube* into a heatproof jug, add 750ml (3 cups) water boiling water and stir to dissolve.
Step 2 — Cook vegetables
Heat 2 tsp olive oil in a large saucepan over medium-high heat. Cook the garlic and onion, stirring, for 3-4 mins until softened. Add the potato, celery, carrot and stock and bring to the boil. Reduce the heat to medium and simmer, covered, for 10-12 mins until the vegetables are almost tender.
Step 3 — Cook fish
ADD PRAWNS OPTION Add the tomato, fish and 3 tsp Greek seasoning* to the soup and bring to a gentle simmer. Reduce the heat to medium-low (or low, if needed, to maintain a gentle simmer) and cook, covered, for 4 mins. Add the prawns and cook for a further 2-3 mins until the prawns and fish are just cooked through and the vegetables are tender.
Step 4 — Toast baguette
Meanwhile, preheat the grill to medium-high. Halve the baguette through the middle. Put on an oven tray, cut-side up. Brush with 2 tsp extra virgin olive oil and season with salt. Grill the baguette, turning halfway, for 4 mins or until golden.
Step 5 — Season soup
Add the parsley, lemon zest and 2 tbs lemon juice to the soup. Taste, then season with salt and pepper. Remove from the heat.
Step 6 — Flake fish and serve
Flake the fish in the soup into bite-sized chunks with two forks. Serve the soup with the crusty bread.