Cover the Chermoula Seasoning with the vinegar and water, set-aside until cool.
Combine fish and the Chermoula paste in a bowl.
Steam potatoes until nearly tender. Heat oil in a flameproof tagine or large heavy-based frying pan with a lid over medium heat. Add onion and red peppers.
Remove fish fillets from Chermoula marinade.
Cook, stirring for 5 minutes or until softened. Add ginger and tomatoes. Cook, stirring for 2 minutes. Add remaining Chermoula marinade, remove from heat and place in a separate bowl.
Arrange potatoes in base of tagine or frying pan. Spoon over half the tomato mixture. Top with fish. Spoon over remaining mixture and stock. Scatter with olives and lemon. Cover with tagine lid or, if using a frying pan, a tight fitting lid. Simmer gently over a medium heat for 10 minutes or until fish is just cooked.
Serve with salad and crusty bread.