Preheat the oven to 375°F.
Heat the olive oil in a large pot or Dutch oven over medium-high heat. Add the beef, season with salt and pepper, and brown on all sides.
Add the pumpkin, onions and garlic and cook until softened, about 10 minutes.
Add the tomato paste and mix. Cook for an additional 1 to 2 minutes.
Transfer the mixture to a large bowl and return the pot to the stove. Lower the heat to medium-low and add the butter. Once the butter is melted, add the flour to the pot and whisk for about 1 minute.
Add the beef broth and milk and whisk until thickened over a simmer, about 5 minutes. Add the beef mixture back into the pot with the peas and stir to combine.
Spoon the mixture into a large cast-iron skillet or baking dish.
Bake for 20 to 25 minutes, until the pumpkin is tender and the sauce is bubbling. Remove from the oven and let sit for 10 minutes to cool.
Place the mashed potatoes in a pastry bag or a plastic bag with the end snipped off. Pipe potatoes in the shape of a ghost on top of the stew. Garnish with the peas as the “eyes."