Heat the oil in a large nonstick frying pan or sauté pan. Fry the onion and peppers over a medium high heat for 5 minutes or until the onions have softened and are beginning to brown, stirring regularly. Add the garlic and cook for a further minute, stirring constantly. Brown the chicken thighs with the vegetables for a further 2-3 minutes until lightly coloured, turning every now and then. Stir the chorizo and rice into the pan and add the saffron and chicken stock. Season well with black pepper and bring the stock to a simmer. Cook for 25 minutes until the rice is tender and almost all the liquid has evaporated, stirring occasionally. Make sure the chicken is cooked through with no pink showing. Add the frozen peas and cook for 1 minute until thawed. Stir the seafood into the rice, along with any of its thawing liquid. Cook over a high heat for 2-3 minutes without stirring until the seafood is completely hot and the paella is becoming lightly browned on the bottom. Serve immediately with fresh lemon wedges for squeezing.