Heat stock in a large pot then add in the saffron threads and et aside.
Pat the cod, shrimp and scallops with kitchen paper to dry. Keep them separate.
In a small blender or processor combine the salt, parsley, garlic and thyme and blitz to a paste. Add a splash of water if needed. Stir in the smoked paprika.
If cooking on an outside grill light the charcoal about 30 minutes before you wish to cook. If using the stove top proceed by heating the paella pan to a medium heat, adding 6 tbsp. of olive oil.
When the oil is hot add the hard chorizo and cook for 2-3 minutes. This releases all the flavorful oils in the chorizo. Remove the chorizo and set aside.
Brown the cod for just 1 or 2 minutes then remove and set aside. It will finish cooking later. Sear the scallops on both sides for a minute or two and remove also. Cook the chicken until sealed and lightly browned. Remove and set aside.
Increase the heat a little then add in the additional 2 tbsp of oil. Ad the onion, scallions and bell pepper to the pan and cook until softened, Add the tomato and cook until sauce like, about 5 minutes. Pour in the seafood stock and bring to a boil. Sprinkle the Arborio rice evenly over the mixture and boil for 3 minutes, giving it an occasional stir.
Add back both the cod, chorizo and chicken. Stir in the parsley paste mixture. Check for seasonings. From this point on DO NOT STIR. Lower the heat to a simmer and continue to cook for about 10 minutes. Add a splash of stock if needed to prevent drying out.
Arrange the shrimp, scallops, clams and mussels over the top. For the mussels and clams place them so the edges will open facing up. Cook uncovered for 15-20 minutes and the rice is almost done. Test a piece of the rice. Remove the pan from the heat and cover with foil and let sit for 10 minutes. Discard any clams or mussels that have not opened.
Garnish with lemon wedges and serve.