Heat oil in a large heavy pot over medium heat. Cook onion, stirring occasionally, until golden and softened (6-8 minutes). Add garlic and cook (stirring often) until fragrant and garlic is softened, about 2 minutes.

Add white wine and cook (stirring often) until the smell of the alcohol is almost completely gone, about 4 minutes.

Add tomato sauce and chopped tomatoes and increase heat to medium-high. Cook, stirring often, until sauce thickens slightly, 8-10 minutes. Taste and season sauce with salt.

Meanwhile, cook noodles/pasta in a large pot of boiling salted water, stirring occasionally, until very al dente, about 3 minutes less than package directions. Drain, reserving 1 cup noodles cooking liquid.

Use the noodles cooking liquid to cook the mussels, clams and shrimp, in a large pot. Cover and cook, shaking the pot occasionally, until mussels open, about 4 minutes. Using tongs, pick out shrimp and mussels and transfer to a large bowl, discarding any mussels and clams that have not opened (important!).

Add the seafood, frozen peas and butter (butter mellows the acid from the fresh onion and the tomatoes) and cook for another 4-5 minutes. Mix in parsley and lemon juice.

Transfer the noodles into the pot, stir to mix well with the sauce. Top with the chopped parsley, serve immediately.