Bring a large pot of salted water to a boil. Add pasta and cook until al dente, 8 to 9 minutes (or according to package instructions). Drain pasta, reserving 1/2 cup cooking liquid. Return pasta to pot and toss with cooking liquid. Cover to keep warm; set aside.

In a large, heavy saute pan or medium pot, heat oil over medium heat. Add pancetta and cook, stirring, 2 minutes. Add onions and cook, stirring, until soft, 3 minutes. Add garlic, parsley, 1/2 teaspoon salt, and red pepper and cook, stirring, 1 minute. Add wine and cook for 1 minute. Add clams and cover; shaking occasionally, cook until clams open, about 5 minutes. Uncover and discard any unopened clams.

Add cooked pasta and toss to coat. Season with salt and pepper. Drizzle with extra-virgin olive oil, add parsley, and toss to coat. Divide among serving bowls and top each portion with cheese, if desired. Serve immediately.