Preheat the oven to 400 degrees and line a sheet tray with non stick foil or parchment. Drizzle the olive oil over the cut side of the butternut squash and season with salt and pepper.
While the squash is roasting, heat 1 Tbsp. of olive oil in a sauté pan set over medium heat and add the diced onion. Cook until softened and golden, about 5 mins, then add the minced garlic.