Preheat oven to 375 degrees.
Set a 14-inch paella pan or a 14-inch ovenproof sauté pan over medium-high heat and add 2 tablespoons olive oil. Season shrimp with 2 teaspoons pimenton and 1/2 teaspoon salt.
Once oil is hot, sear shrimp, about 1 minute per side. Remove shrimp from pan and set aside.
Add remaining olive oil and chorizo to pan and sear, stirring occasionally, until sausage is nicely browned, 1 to 3 minutes.
Add onions, bell peppers, garlic, and saffron to pan and sauté, stirring often, until lightly caramelized, 6 to 7 minutes.
Add rice and cook, stirring, 3 minutes. Season with remaining salt and pimenton. Add stock to pan, bring to a boil, reduce heat to a simmer, and cook, undisturbed, until rice is no longer soupy but some liquid still remains, 5 to 6 minutes.
Give rice a quick stir, then add clams with opening edges facing up. Reduce heat to low and continue to simmer for 5 minutes. Add peas, mussels (opening edges facing up), and shrimp to pan and continue to cook, untouched, 10 minutes.
Transfer pan to oven and cook until clams and mussels have opened, liquid is mostly absorbed, and rice is almost cooked through, about 10 minutes.
Remove paella from oven and cover with foil. Let sit for another 10 minutes before serving, so that the rice will continue to cook and absorb liquid. Serve garnished with parsley and topped with a few lemon wedges.