Bring a large pot of generously salted water to a boil. Cook the spaghetti until just al dente according to the package directions, reserve 1 cup of pasta water, and drain.

While the pasta cooks, place the finely chopped bacon in a large skillet over medium heat. Cook for 5–7 minutes until browned and crisp, then transfer it to a paper-towel-lined plate, leaving about 1 tablespoon of bacon fat in the skillet.

Pat the scallops very dry and season lightly with salt and pepper. Add the olive oil to the skillet, increase the heat to medium-high, and sear the scallops in a single layer for 2–3 minutes per side until deeply golden and nearly cooked through; transfer them to a plate.

Reduce the skillet heat to medium. Add the butter and garlic, cooking for about 30 seconds until fragrant without allowing the garlic to brown.

Pour in the wine or broth and scrape up the browned bits from the bottom of the pan. Simmer for 1–2 minutes.

Stir in the heavy cream and optional red pepper flakes. Simmer gently for 3–5 minutes, until the sauce is slightly thickened.

Lower the heat and whisk in the Parmesan. Add the drained spaghetti and toss until coated, loosening the sauce with reserved pasta water 1–2 tablespoons at a time as needed.

Fold most of the bacon into the pasta. Return the scallops to the skillet and warm them gently for about 1 minute.

Finish with parsley, black pepper, and optional lemon juice. Serve immediately with the remaining bacon and additional Parmesan.