Place chopped potatoes in a large pot and cover with cold, salted water. Bring to a vigorous boil and cook for about 15 minutes until fork-tender. Drain and let steam dry for a minute.

In a mixing bowl, mash the hot potatoes until creamy. Add butter, milk, garlic powder, salt, and pepper. Combine until smooth and let cool slightly.

In a large skillet, heat olive oil over medium. Add diced onion and minced garlic, sauté for 2-3 minutes until onion is translucent.

Stir in ground beef, breaking it apart. Cook until browned, about 5-7 minutes. Mix in tomato paste, Worcestershire sauce, mixed vegetables, and broth. Season and simmer until thickened, about 5-7 minutes.

Preheat oven to 375°F (190°C). Spoon beef mixture into a 9x9 baking dish, smoothing the top.

Using a piping bag, pipe ghost shapes of the mashed potato mixture over the beef filling. Dot with peppercorns for 'eyes'.

Bake in preheated oven for 20-25 minutes until the mashed potatoes are golden and the filling is bubbly.