Heat olive oil in a large paella pan or wide skillet over medium heat.
Add the chopped onion and diced red bell pepper; sauté for 5 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Stir in the rice, smoked paprika, and saffron with its soaking water; cook for 2 minutes, stirring to coat the rice with oil and spices.
Pour in the seafood stock and add the diced tomatoes. Stir to combine and bring to a gentle boil.
Reduce heat to medium-low and simmer uncovered for 15 minutes without stirring.
Arrange the shrimp, mussels, clams, and squid rings evenly over the rice. Sprinkle the frozen peas on top.
Cover the pan with a lid or aluminum foil and cook for another 10-15 minutes, until the seafood is cooked through, the mussels and clams have opened, and the rice is tender.
Discard any unopened mussels or clams. Season with salt and freshly ground black pepper to taste.
Remove from heat and let the paella rest covered for 5 minutes.
Garnish with chopped fresh parsley and lemon wedges before serving.