Dry-fry coriander and cumin seeds over medium heat for 2 minutes until aromatic.
Blend seeds with remaining spice mix ingredients into a paste.
Sauté onion, celery, carrot, and garlic in olive oil for 6 minutes until soft.
Add potatoes, tomatoes, and spice paste then fry for 8 minutes.
Add one ladle of stock and chopped peppers, boil for 1 minute, then add remaining stock.
Stir in chilli, olives, orange zest, and juice, then simmer covered for 30 minutes.
Create chermoula by crushing toasted seeds and mixing with lemon, orange zest, and coriander.
Marinate the mixed seafood in the chermoula for 10 minutes.
Toast harissa spices and blend with remaining harissa ingredients into a paste.
Prepare couscous with butter and water, then fluff and stir in remaining couscous ingredients.
Steam green beans for 3 minutes until tender and top with almonds and oil.
Add marinated seafood to the tagine and simmer for 4 minutes until cooked.
Serve fish tagine with harissa couscous, green beans, and coriander garnish.