Bring a large pot of salted water to a boil. Cook penne pasta according to package directions until al dente, about 8-10 minutes. Drain and set aside, reserving 1/2 cup of pasta water.

While the pasta cooks, heat olive oil in a large skillet over medium-high heat. Add diced onion and cook for 3-4 minutes until softened and translucent. Stir in minced garlic and cook for an additional 30 seconds, until fragrant.

Add the ground beef to the skillet, breaking it up with a wooden spoon. Cook for 6-8 minutes until completely browned with no pink remaining. The beef should reach an internal temperature of 160°F. Drain excess fat if necessary.

Stir in the diced tomatoes with juices, beef broth, and Italian seasoning. Bring to a gentle simmer and let it cook for 5 minutes to develop flavors and reduce the liquid slightly.

Remove the skillet from heat and let it cool for 2 minutes to prevent the Greek yogurt from curdling. Slowly whisk in the Greek yogurt until completely smooth. Add in the Parmesan cheese and stir until melted.

Toss the cooked pasta into the beef mixture until well coated. If the sauce seems thick, add reserved pasta water one to two tablespoons at a time until you reach the desired consistency. Finally, season with salt and pepper to taste.