Step 1 Bring a large pot of lightly salted water to a boil.
Step 2 Heat the olive oil in a skillet over medium heat. Add the chorizo and cook until it begins to brown and render fat, about 5 minutes. Add the white wine and increase the heat to high. When the wine is bubbling, add the mussels, cover and cook until the shells open, about 5 minutes. Add the calamari and cook until the edges curl, about 1 minute. Remove from the heat.
Step 3Use a slotted spoon to transfer the chorizo, mussels and calamari to a bowl, cover tightly and refrigerate until needed. Add the saffron threads to the liquid in the pan and return to the heat. Simmer until the liquid is reduced by half to about one-third cup.
Step 4Place the red onion in a strainer and rinse under cold water to remove some of its "bite."
Step 5Cook the rice as you would pasta: Add the rice to the boiling water and cook until it is tender, 10 to 15 minutes. Do not overcook or undercook it; the rice should be soft all the way through but should not be beginning to "explode" at the ends.
Step 6Line a jellyroll pan with a kitchen towel. Drain the rice and rinse it quickly under cool water, then spread it over the kitchen towel. Cover with another kitchen towel and gently pat dry.
Step 7Transfer the rice to a large mixing bowl. Pour the saffron liquid over the rice, add the red onion and stir gently with a wide rubber spatula to coat evenly. The rice should be a uniform golden color. Season to taste with about 1 teaspoon of salt, and set aside to cool completely. (The recipe can be prepared to this point up to 1 day in advance and refrigerated tightly covered; bring the rice back to room temperature before finishing the recipe. You may need to add a little olive oil to finish.)
Step 8Add the red pepper strips, lemon juice, parsley, chorizo and calamari to the rice, and stir gently to mix well. Season to taste. Transfer to a large, flat serving bowl, and scatter the cooked mussels over the top. Serve at room temperature.