Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish and set aside.
Heat olive oil in a large skillet over medium heat. Add onion and cook 3-4 minutes until softened. Stir in garlic for 30 seconds. Add ground beef and cook until browned, breaking into crumbles. Drain excess fat if needed and season with paprika, oregano, salt, and pepper.
In a medium bowl, whisk together the Greek yogurt, light sour cream, and cornstarch until completely smooth.
Arrange half of the sliced potatoes in an even layer in the prepared dish. Top with half the beef mixture, half the yogurt mixture, and half the cheddar.
Repeat with remaining potatoes, beef, yogurt mixture, and cheddar.
Slowly pour the beef broth around the edges and evenly over the casserole.
Cover tightly with foil and bake for 45 minutes.
Remove foil and continue baking 15-20 minutes, until potatoes are fork-tender and cheese is melted and lightly golden.
Let rest 10 minutes before serving. Garnish with chopped parsley.
Notes
Refrigerate leftovers up to 3-4 days. Reheat covered in a 325°F oven for 20-30 minutes, or microwave individual portions. Freezes well up to 2 months; thaw overnight in the refrigerator before reheating. Ground turkey can be substituted for beef.