Cook the spaghetti in a large pot of salted boiling water according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the spaghetti.
In a large skillet, heat the olive oil over medium heat. Add the diced pancetta or turkey bacon and cook until crispy, about 5-7 minutes. Add the minced garlic in the last minute, sautéing until fragrant.
In a bowl, whisk together the eggs, grated Parmesan cheese, and black pepper until well combined.
Remove the skillet from heat and add the drained spaghetti to the skillet, tossing to combine with the pancetta and garlic.
Quickly pour the egg and cheese mixture over the hot pasta, tossing vigorously to create a creamy sauce. If the sauce is too thick, add reserved pasta water a little at a time until you achieve the desired consistency.
Season with salt to taste and mix until everything is well coated and creamy.
Serve immediately, garnished with chopped parsley and extra Parmesan cheese if desired.