In a Dutch oven, heat the olive oil over medium heat. Add the chorizo and cook until it releases its fat. 8 to 10 minutes. Add the chicken, onions and garlic and brown the chicken on all sides, about 10 minutes.
Add the rice and toast for 30 seconds. Add the tomato paste, followed by the saffron and then the wine, stirring. Add the chicken stock, cover and cook--no stirring--for 20 to 25 minutes. By then the rice should be almost done.
Add the shrimp, mussels and peas and continue to cook until the rice is fluffy and the mussels have opened. Season with salt and pepper. Finish with the scallions and serve.