Preheat oven to 400 degrees.
To a small mixing bowl, add dressing ingredients (add only ¾ tsp salt at this time) and mix with a spoon to combine.
To a baking sheet, arrange butternut squash, cauliflower, and onion in a single layer. Pour the prepared dressing atop the vegetables on the baking sheet and, using a spoon or your hands, coat vegetables in dressing. Transfer baking sheet to oven and bake for 20 minutes.
After baking for 20 minutes, remove baking sheet from oven, add bacon pieces and, using tongs, incorporate pieces into the vegetables and dressing. Return baking sheet to oven and bake for additional 25 minutes. After 25 minutes, check bacon, especially if you're using thicker slices. If it still looks like bacon needs to cook a little longer, continue baking until desired crispiness is reached.
Remove baking sheet from oven, add in spinach and, using a spoon, gently stir to mix through other ingredients. Return baking sheet to oven to bake until spinach has wilted, about 5 minutes.
Remove baking sheet from oven and allow to cool slightly before carefully taste-testing. Based on your preferences, add additional ¼ tsp salt. Serve with sour cream.
