In a Dutch oven or large, heavy-bottomed pot, heat the olive oil over medium-high heat. Add the pancetta, and cook for 5 minutes or until browned. Using a slotted spoon, remove the pancetta and set aside, leaving the rendered fat in the pot.
Add the celery, onion, carrots, jalapeno, and garlic to the pot, and stir. Cover and cook for 15 minutes, stirring occasionally. Add the ground beef, black pepper, and cayenne pepper. Stir to combine and then cook, uncovered, for 10 minutes.
Stir in the broth, tomato paste, and pancetta. Cook, covered, on medium-low heat for 45 minutes, stirring occasionally and making sure to scrape the bottom of the pot.
Just before serving, stir in the Greek yogurt. (If you prefer a dairy-free version, you can omit the yogurt; it will just be slightly less creamy.) Serve over spaghetti squash or spaghetti, and top with a sprinkle of Parmesan cheese, if using.