Cut the sausage into 1-inch chunks. Set the paella pan over the grill to heat for a minute and add the sausage. Cook, stirring occasionally, until the sausage begins to brown and renders some of its fat, about 5 minutes.
Add the onion and saffron to the pan and cook, stirring occasionally, until the onion softens slightly, about 3 minutes.
Add the garlic and rice, and stir until the rice is translucent, about a minute, and then add 4 cups of chicken stock. Bring to a boil, and then turn the grill to medium low, close the cover, and cook, stirring once or twice until the water is absorbed, about 20 minutes. Check the rice and if it’s still too firm, add more chicken stock. Continue cooking until the rice is cooked through.
When the rice is cooked and has absorbed the water, stir in the peas and then nestle the cooked chicken into the rice so that it will heat, and the shrimp over the top of the rice to cook. Close the grill and turn the heat to high, Stop stirring and cook for a few more minutes just until the shrimp has cooked through, about 3 to 5 minutes. Remove from the grill and sprinkle with parsley before serving.
