Bring a large pot of water to a boil and salt it generously.
Heat 2 tablespoons of the olive oil in a large skillet over medium-low heat. Add the panko and cook, stirring, until golden brown, 2 to 3 minutes. Immediately transfer to a bowl, stir in the oregano, season the crumbs lightly with salt, and set aside. Wipe out the skillet.
Drop the pasta into the boiling water, stir, and cook until just al dente, according to package instructions.
Return the skillet to medium heat and add the remaining olive oil and the pancetta. Cook, stirring frequently, until golden brown and crisp. Transfer to a small bowl using a slotted spoon and set aside. Add the onions to the skillet and cook, stirring, until softened, 2 to 3 minutes. Stir in the garlic and cook for about 2 minutes more.
Increase the heat to medium-high and pour in the wine. Let it simmer until nearly evaporated, about 1 minute. Add the clams with their liquor and cook, stirring, until the clams are cooked through, 30 seconds to 1 minute. Stir in the butter, if using, lemon zest, and parsley and toss until melted and hot.
Remove about 1/2 cup of the pasta cooking water and reserve; drain the linguine and toss it in the skillet. Toss the pasta with the clam sauce using tongs until evenly coated and combined, adding some pasta water or olive oil if the mixture is too dry. Season the pasta with a little salt, if desired, and a healthy grind of black pepper.
Transfer the pasta to a serving platter and scatter some of the breadcrumbs evenly over it. Serve immediately with more breadcrumbs passed at the table.