Heat the oil in a pan and add the onion. Cook on a low heat for 10 minutes.
Stir in the thyme and orange ring, and cook for 1 further minute.
Stir in the tomatoes, olives, sugar, salt and pepper and heat without reaching boiling point.
Put the mixture into a pot and cover with the lid, and cook for 1 and half hrs.
During this time, rinse the skate under cold water and pat dry with kitchen paper.
Sprinkle the flour onto a flat surface and season with salt and pepper.
Coat each wing in the flour, shaking off the excess, then removing the lid, place them on top of the tomato sauce.
Put the lid back in place and reduce the temperate to low.
Cook until the skate is cooked, or when it flakes easily.
Place the fish onto a warm plate and spoon the sauce over it.