Bring a large pot of water to a boil. Add the spaghetti and cook until al dente according to the package directions. Before draining, reserve about ½ cup of the pasta water. (Just scoop it out with a coffee mug; it doesn’t need to be precise and the mug’s handle makes it safer to dip.)
Meanwhile, in a large skillet, cook the bacon over medium heat to your desired crispness. Crumble the bacon. Pour off all but 1 teaspoon of the bacon grease from the skillet. Return the bacon to the pan.
Add the kale and peas and cook for 5 minutes, stirring often, until the kale wilts and the peas thaw and warm up. Add the garlic, then remove the skillet from the heat and let cool for 3 to 5 minutes.
Now comes the tricky part: Add the hot pasta to the skillet, then add the beaten egg and very quickly mix together. If you’re not quick, you’ll get scrambled eggs and not sauce. If this happens, don’t fret . . . just mix very well and most of the lumps will dissolve. Add ¼ cup of the reserved pasta water and mix well. Add more pasta water if needed to thin out the sauce.
Top with half the Parmesan and half the parsley. Toss to combine, then top with the remaining Parmesan and parsley and serve.