The chicken should marinade for about 2 hours. To make the marinade, combine 2 tbsp olive oil, paprka, oregano, salt and pepper. Stir in chicken pieces to coat. Cover and refrigerate. (We like to use 1 gallon freezer bags.)
Heat 2 tbsp oil in a large skillet over medium heat. (You could use a traditional paella pan, but we don't have one, so we used a risotto pan.) Add garlic, red pepper flakes, and rice. Cook, stirring, to coat rice with oil, about 3 minutes. Sir in saffron threads, bay leaf, parsley, chicken stock, and lemon zest. Bring to a boil, cover, then reduce heat to medium low. Simmer 20 minutes.
Meanwhile, in a separate skillet, heat the remaiining 2 tbsp oil over medium heat. Stir in marinaded chicken and onion. Cook 5 minutes, then add bell pepper and sausage. Cook 5 more minutes. Stir in shrimp and cook, turning, until both sides of the shrimp are pink.
Spread the rice into a large serving dish. Traditional paella pans are large enough to serve with, but we used a cast iron pan that we use to broil turkey instead.) Top with meat and seafood mixture.
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