In a small bowl, crush the saffron threads into the seafood stock and let it steep while you prepare the other ingredients.
Heat the olive oil in a small paella pan or wide skillet over medium heat.
Add the diced onion and red bell pepper, sautéing for 3-4 minutes until the vegetables are softened and fragrant.
Stir in the minced garlic, smoked paprika, and diced tomatoes, cooking for another 2 minutes to create a thick base called a sofrito.
Add the dry Bomba rice to the pan, stirring constantly for 1 minute to toast the grains and coat them in the sofrito.
Pour in the saffron-infused seafood stock and season with sea salt and black pepper; bring to a gentle simmer.
Reduce heat to low and cook undisturbed for 10-12 minutes, allowing the rice to absorb most of the liquid.
Arrange the shrimp and mussels on top of the rice, pressing them down slightly into the liquid.
Cover the pan and cook for another 5-7 minutes until the shrimp are pink and the mussels have opened.
Scatter the frozen peas over the top during the last 2 minutes of cooking.
Remove from heat, let rest for 5 minutes, and serve with a fresh lemon wedge to brighten the flavors.