Heat 1 tablespoon vegetable oil in a large pan over medium heat. Add the 1 medium diced yellow onion and sauté until tender and translucent, about 5 minutes.
Add 40 grams peas and 450 grams mixed seafood plus the tomato sauce to the pan. Stir to combine and cook on medium heat until the seafood is heated through and opaque, about 3–5 minutes.
In a small container, combine 250 ml water with 1 teaspoon saffron and stir to release the color. Pour the saffron water into the pan, add 1 teaspoon smoked paprika, bring to a simmer, and cook until the liquid reduces slightly, about 4–6 minutes.
If the 450 grams cooked rice is cold, warm it in the microwave. Add the rice to the pan, stir gently to combine, and simmer for 5 minutes so the rice heats through and absorbs flavor. If using the red bell pepper, add thin slices now.
Taste and season with salt to taste. Remove from heat, garnish with chopped fresh parsley, and serve with lemon wedges.