Cut the pumpkin into large bite-sized pieces. Place in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 2 minutes and 30 seconds. Slice the onion into 5mm slices.

Heat olive oil in a frying pan over medium heat. Add the pumpkin and cook until browned, then remove from the pan.

In the same pan, add the beef and grated garlic. Stir-fry over medium heat until the beef changes color. Add the onion and cook until softened. Return the pumpkin to the pan and add the seasonings (ketchup, mustard, salt, pepper, oregano). Stir-fry everything together.