Heat the oven to 375F.

Place the sausage, red onion, and butternut squash on a rimmed sheet pans (you may need to use two sheet pans to avoid over-crowding). Drizzle with olive oil, sprinkle with ½ teaspoon salt, and toss to combine.

Place the pans in the oven and roast for 15 minutes. Remove from the oven and stir the mixture gently. Return to the oven and roast an additional 10 minutes, or until everything is golden and cooked through.

Remove from the oven and allow to cool. Turn the heat down to 350F.

Whisk the eggs together with the cooled, roasted veggies and the spinach in a large bowl along with ½ teaspoon salt.

Pour the egg mixture into a 12-cup muffin tin (use silicone liners to avoid sticking), dividing the mixture evenly between the cups. The mixture should come near to the top of each cup.

Bake for 20-25 minutes, or until puffed and cooked through.

Remove from the oven and allow to cool. Serve warm, or refrigerate in a tightly sealed container for up to 4 days.

Alternatively place the cooled cups on a baking sheet in the freezer. Allow to freeze completely, then place in a zip top bag or tightly sealed container for up to a month.