Squeeze the lemon juice over the bream and sprinkle Cajun seasoning over one side of the fillets. Wrap loosely in foil and bake in the oven for 15 minutes.
Steam the sweet potato for 20 minutes.
While the sweet potato is cooking, heat 2 tablespoons of the tea oil in a large frying pan and add the onions. Fry the onions, stirring them regularly until they turn dark brown and sticky. Add the preserved lemon and season with black pepper.
Mash the sweet potato until smooth with the remaining tea oil.
Serve the onion over the sweet potato with the bream fillets over the top.
Serve with a green salad.
Note: Onions are a natural antibiotic and can be effective in destroying unhealthy bacteria in the gut.