Preheat oven to 400 degrees Farenheit. Lightly oil a baking sheet or line with parchment paper.
Combine mashed butternut squash with peanut butter.
In a large bowl, combine the mixture with ground beef and the seasonings. Mix gently using hands, taking care not to overwork the meat. Shape into 1 ½ inch balls.
Place on baking sheet. In a small oven-safe dish(es), add some water and place in the pan alongside the meatballs.
Bake for 15-20 minutes, flipping halfway through. Inserted thermometer should read 160 degrees Fahrenheit.
Store in an airtight container for 3-5 days in the fridge.
Freeze for up to 3 months. I personally flash freeze all my baked goods.
To reheat, place in a skillet with a splash of liquid (e.g. water, broth, sauce, etc.). Cover and heat over medium-low heat until warm, 2-3 minutes or so. This is to ensure meatballs don't get dried out.