Pour stock into a medium saucepan and heat on low until warm.
Meanwhile, heat oil in a large frying pan or paella pan. Add the onion and garlic and sauté for 2-3 minutes until the onion is beginning to soften. Add the chopped chorizo and red pepper and continue to cook for an additional 5 minutes until the onion is soft and the chorizo has released oil and is starting to brown.
Add the rice and stir to combine with the onion, garlic and chorizo until all the rice is coated in oil. Continue to cook for approximately 1 minute.
Add the saffron, paprika, and wine. Bring to a boil and cook for 1-2 minutes until wine starts to reduce. Add enough stock to cover the rice. Stir and bring to a simmer. Continue to cook on low simmer for about 12 minutes, stirring occasionally. Pour in more stock as needed if rice begins to look dry.
Add shrimp, pushing them into the rice. Nestle the clams in the rice, with the connected part of the clam shell facing down into the rice. Add a few grinds of black pepper, if desired. (I usually do not add any salt as I find the chorizo is enough.) Add the remaining stock and cover the pan tightly with foil. Leave on low heat and cook on low summer for 10 minutes.
Remove foil and sprinkle the peas all over the paella. Taste for seasoning and add more salt and pepper if desired. Cover again with foil and continue to cook until the rice is tender, the prawns are fully cooked and the clams have opened. Note: If you would like some browning on the bottom, you can up the heat to medium high. (Discard any unopened clams.)
Serve immediately with chopped parsley and lemon wedges.