• Gather all ingredients and preheat oven to 400°F (200°C).

For the Meat Filling:

• Heat the olive oil in a large skillet over medium-high heat for a couple of minutes, then add the chopped onion and cook until softened, about 5 minutes, stirring occasionally.
• Add the ground beef (or lamb) and break it up with a spoon. Stir in the dried parsley, rosemary, thyme, salt, and black pepper. Continue cooking until the meat is well browned, about 6–8 minutes.
• Mix in the Worcestershire sauce and minced garlic and cook for about 1 minute to release the garlic aroma.
• Sprinkle in the flour and add the tomato paste, stirring thoroughly until the paste is fully incorporated and no lumps remain.
• Pour in the beef broth, add the frozen peas and carrots and corn, raise to a boil, then lower the heat and simmer for about 5 minutes until the mixture thickens slightly. Remove from heat and set aside.

For the Potato Topping:

• Place the cubed potatoes in a large pot and cover with cold water. Bring to a boil, then reduce to a simmer and cook until the potatoes are fork-tender, about 10–15 minutes.
• Drain the potatoes in a colander, return them to the hot pot, and let them sit for about 1 minute so excess steam can evaporate.
• Add the butter, half & half, garlic powder, salt, and black pepper to the potatoes. Mash until smooth and all ingredients are evenly combined.
• Fold the Parmesan into the mashed potatoes until well distributed.

To Assemble and Bake:

• Spread the meat mixture in an even layer in a 9x9-inch (or 7x11-inch) baking dish.
• Spoon the mashed potatoes over the meat and gently smooth or spread into an even layer. If the dish seems very full, set it on a rimmed baking sheet to catch any bubbling over.
• Bake uncovered at 400°F (200°C) for 25–30 minutes, until the top is golden and the filling is bubbling. Let cool for about 15 minutes before serving.