Bring a large pot of salted water to a boil and cook the 12 oz spaghetti until al dente. Before draining, reserve about 1 cup of the pasta water.
While the pasta cooks, heat 1 tablespoon olive oil in a large skillet over medium heat. Add the 6 oz chopped turkey bacon and cook until crisp, about 5 to 6 minutes, adding the 2 cloves crushed garlic in the last minute if using. Turn off the heat.
In a bowl, whisk together the 2 eggs, 2 egg yolks, 1 cup grated Parmesan, and 1 teaspoon black pepper until smooth.
Add the hot, drained spaghetti to the skillet with the turkey bacon and toss. Off the heat, pour in the egg-and-cheese mixture and toss constantly, adding splashes of the reserved pasta water until the sauce is silky and coats the pasta.
Taste, season with salt and more pepper, and serve right away with extra Parmesan and parsley.
