Peel the potatoes & cut them into strips, about the size of a large french fry. Put them into a bowl & rinse. Then sprinkle paprika over the potatoes, turning them several times to make sure they are all covered.
Place the tomato sauce, olive oil, water, tomato, onions, & spices in a medium or large tagine. Stir to mix all the ingredients, then lay the potatoes on top of the sauce. Cover & cook on low heat for 30 minutes.
While the potatoes are cooking, mix the ingredients of the charmoula in a small bowl. Place the fillets into a shallow bowl or dish, pour half the mixture over top of the fish & let it marinate for 30 minutes.
Boil the olives in a small sauce pan of water for 5 minutes to remove their bitterness. Once done, drain the water & stir the rest of the charmoula in with the olives, set aside to be used later.
Stir the sauce in the tagine then place the fish fillets on top of the potatoes. Scatter the lemon & olives on the fish & pour all the remaining charmoula over the fish.
Cover the tagine & continue to cook on low heat for another hour. The tagine is done once the potatoes are tender.
Serve in the tagine with thick bread to scoop up the sauce & fish. Make sure you protect your table because the tagine will stay hot for a time.