Preheat the oven to 450F or 425F convection (convection is best for roasting!). Line a baking sheet with parchment paper.
Add the squash to the baking sheet and drizzle with oil and sprinkle with salt. Use your hands to toss so that each piece is coated well in oil. Spread into an even layer. Bake for 30-40 minutes, or until the squash is nicely browned.
Bring a pot of water to a boil and add the spinach, let cook until the spinach has wilted down, about 30 seconds to 1 minute. Drain and transfer to a bowl to cool. In a high-speed blender, add the pecans, parmesan, rosemary, garlic, salt, and pepper and blend to finely chop. Drain out any excess liquid from the cooked spinach and add to the blender along with the olive oil, lemon juice, and orange juice and blend until combined. Transfer to a jar or bowl.
Soak the cranberries in boiling water for 5-10 minutes, then drain (this helps plump them up).
Arrange the squash on a large platter. Top with plenty of pesto. Sprinkle cranberries and pecans over top.