In a wide, shallow pan or paella pan, heat the olive oil over medium heat.
Add the diced onion and red bell pepper, sautéing until the vegetables are softened and slightly caramelized.
Stir in the minced garlic and smoked paprika, cooking for 30 seconds until fragrant.
Add the tomato puree and Bomba rice, stirring constantly for 1-2 minutes to toast the rice grains slightly.
Pour in the seafood stock and add the saffron threads, sea salt, and black pepper. Stir once to distribute the rice evenly, then do not stir again to allow a crust (socarrat) to form on the bottom.
Simmer on medium-low heat for about 10 minutes until the liquid is partially absorbed.
Nestle the shrimp, cubed cod, and mussels into the rice. Cover the pan and cook for another 8-10 minutes until the seafood is cooked through and the mussels have opened.
Remove from heat and let the paella rest, covered, for 5 minutes.
Garnish with freshly chopped parsley and serve with lemon wedges for squeezing over the top.