In a medium bowl, mix together 2 tablespoons olive oil, paprika, oregano, and salt and pepper. Stir in chicken pieces to coat. Cover, and refrigerate.
Heat 2 tablespoons olive oil in a large skillet or paella pan over medium heat. Stir in garlic, red pepper flakes, and rice. Cook, stirring, to coat rice with oil, about 3 minutes. Stir in saffron threads, bay leaf, parsley, chicken stock, and lemon zest. Bring to a boil, cover, and reduce heat to medium low. Simmer 20 minutes.
Meanwhile, heat 2 tablespoons olive oil in a separate skillet over medium heat. Stir in marinated chicken and onion; cook 5 minutes. Stir in bell pepper and sausage; cook 5 minutes. Stir in shrimp; cook, turning the shrimp, until both sides are pink.
Spread rice mixture onto a serving tray. Top with meat and seafood mixture.