Seafood Spaghetti with Mussels and Shrimp

Name: Seafood Spaghetti with Mussels and Shrimp
Ingredients: ¼ cup extra-virgin olive oil; 1 medium onion, finely chopped; 4 garlic cloves, sliced; ¾ teaspoon crushed red pepper flakes; 3 tablespoons tomato paste; 1 cup dry white wine; 1 28-ounce can whole peeled tomatoes; Kosher salt; 1 pound spaghetti; 2 pounds mussels, scrubbed, debearded; 2 pounds large shrimp, peeled, deveined; 3 tablespoons unsalted butter; 3 tablespoons finely chopped parsley; 1 tablespoon fresh lemon juice; Lemon wedges (for serving)