1 small butternut squash
1 red onion, sliced in rings 1/4 inch thick
1/4 cup canned beet juice
1 tablespoon white vinegar
1 tablespoon sugar
1/4 teaspoon kosher salt, or to taste

Bake squash 45 minutes or microwave about 5 minutes. Remove seeds, thinly slice, and set aside. Marinate onion in remaining ingredients for an hour.