Preheat your oven to 200°C/Fan 180°C/Gas 6. Peel and thinly slice the onions. Scrub the sweet potato and chop it into 1cm dice.
Pour 1 tsp olive oil into a large pan and warm over a medium heat for 2 mins. Slide the chopped onions and sweet potato into the pan. Sprinkle in a pinch of salt and pepper. Fry for 8-10 mins, stirring occasionally, till the veg are slightly softened and a little browned.
While the veg cook, peel the garlic clove and finely grate or crush it. Peel the ginger and turmeric and finely grate both (you may want to grate the turmeric onto a plate as it stains, see our tip below). Dice the tomatoes.
Slide the chopped garlic, ginger and turmeric into the pan and stir well. Fry for a further 1 min.
Add the tomatoes to the pan. Crumble in the coconut cream and half the stock cube. Pour in 300ml boiling water and stir well to dissolve. Bring to a simmer and cook for 10 mins, till the sweet potatoes are tender.
Meanwhile, pop the pollock fillets into a roasting tin and rub with 1 tsp olive oil. Sprinkle over a pinch of salt and pepper. Slide the fish into the hot oven and roast for 12-15 mins, till the fish flakes easily when pressed.
Taste the curried sweet potatoes and add a pinch of salt if needed. Spoon the curried sweet potatoes into a couple of warm bowls and top with a pollock fillet each to serve.