Preheat your oven to 375°F (190°C).
Peel and chop the carrot, parsnip, and turnip into uniformly sized cubes. Toss them in a bowl with olive oil, chopped rosemary, salt, and pepper.
Spread the seasoned root vegetables evenly in a baking dish and roast in the oven for 20 minutes.
While the vegetables roast, heat a skillet over medium heat. Add the lean ground beef and season with salt and pepper. Cook until the beef is browned and crumbled, about 5-7 minutes.
Meanwhile, peel the golden potato and boil until tender, about 15 minutes. Drain and mash the potato with a fork until smooth. Stir in the non-fat Greek yogurt to achieve a creamy texture, and season with a pinch of salt and pepper.
Remove the roasted vegetables from the oven, and mix in the cooked ground beef. Transfer the mixture back to the baking dish, smoothing it out into an even layer.
Carefully dollop and then gently spread the creamy mashed potato mixture on top of the beef and vegetable base.
Return the dish to the oven and bake for an additional 10-12 minutes until the topping is set and beginning to turn golden.
Remove from the oven and let cool for a few minutes before serving.