For the romesco: Heat the oven to 200C.
Place the tomatoes and garlic in a small ovenproof dish. Add 1 tablespoon of the oil and place in the oven for about 10 minutes or until the tomatoes are bursting and browned and the garlic is browned and tender.
For the paella: Place the chicken, 2 tablespoons of the oil and the oregano in a mixing bowl. Crush one of the cloves of garlic with ¼ teaspoon salt with the side of a knife and add this to the chicken. Mix well and reserve.
Heat the remaining oil in a small heatproof frying pan over moderate heat and add the remaining garlic, the onion, carrot, celery, pumpkin and ½ teaspoon salt. Mix well. Fry gently without browning for 10 minutes or until the onion is soft.
Add the rice, mix well and stir-fry for 1 minute.
Add the saffron and water, the stock and water. Bring to the boil and boil gently for 15 minutes or until the rice is just tender and the liquid almost all absorbed. Stir in the beans and peas. This is the paella.
For the chicken: While the rice is cooking, heat a barbecue or ridged grill over moderate heat and place in the chicken thighs, side by side. Cook gently for about 8 minutes on each side, remove from the barbecue or grill and slice 2cm thick across the grain of the meat.
Serve the sliced chicken on the rice with the romesco on top.