First off, dry the defrosted seafood using a kitchen towel or similar, and cut the calamari into rounds.
Fry the finely chopped onion and a clove of chopped garlic in a tablespoon of olive oil in a deeper pan or pot with a lid. Give it a couple of minutes on a low heat until it takes on a little colour.
Add the rice and sauté for another minute. Then add the sweet and smoked paprika and sauté again for a minute.
Add the crushed tomatoes, salt and pepper and sauté again for a minute. Dice and add the peppers, then the frozen peas, and pour in the stock so that the rice is completely covered with liquid.
Add the saffron and cook over a low heat, gradually adding the stock as it is absorbed and evaporates. Stir occasionally.
About halfway through cooking, when there is little more than a residue of unabsorbed stock, put on a low flame, cover and cook the rice under the lid until soft.
Now it's time to sear the seafood on a high heat in a second pan. Shrimp need no more than 2 minutes a side. One minute a side for calamari. This way everything stays juicy and delicate.
Serve the paella right in the pan with the seafood piled on top; garnish with rosemary and lemon.