Make a fish stock with the rock fish and salted water. Put in the tomatoes for the first 15 minutes of cooking time, after which they can be taken out and skinned.
Put the paella pan over the heat, heat the olive oil and fry the ñora (without its seeds), then the tuna, cut into four large chunks, and finally, briefly, the prawns in their shells. Remove the ñora, fish and shellfish from the pan.
Peel the head of garlic. Crush the ñora with a mortar and pestle (or food processor), add half the head of garlic and crush again. Once everything is pounded, add half the tomatoes. Chop the other half of the head of garlic with the prawns. The dish can be prepared ahead of time up to this point.
Put the paella pan back over the heat and fry the prawns and garlic together. Add and briefly fry the rice, add the fish stock and then the picada of ñora and garlic. Put the chunks of tuna and the whole prawns on top of the rice. Leave to cook over slow heat for approximately 15 minutes, and to rest for 5 minutes before serving.