Add the minced onion and sauté for 5 minutes or so until golden.
Add the ginger, garlic, curry paste and butternut squash. Mix to coat the butternut squash in the curry paste. Sauté for a couple of minutes to bring out the aroma of the spices.
Add the beef stock, coconut milk, fish sauce and mushrooms. Bring to a simmer.
Simmer until the butternut squash is almost cooked for 10 to15 minutes, then add the spinach and beef and simmer for 5 minutes more.