Preheat the oven to 425 degrees F.
Slice the squash in half, lengthwise. Remove skin from the outside using a peeler. Remove the seeds from the inside.
Place one squash on a cutting board, cut side down. Use a sharp knife to make slices through the rounded sides of squash, about 1/8 inch apart, going as deep as possible but without cutting all the way through. *Position butter knives or wooden spoons on each side of the squash to prevent cutting all the way through.
Gently place the sliced squash onto a lined baking sheet. Season all sides with olive oil, salt and pepper. Roast for 15 minutes.
Meanwhile, in a small saucepan over medium high heat, melt butter. Then stir in brown sugar, chopped sage and Pumpkin Pie Spice. Once ingredients are combined, remove from heat.
Remove squash from oven at the 15 minute mark. Use a pastry brush to generously apply the butter mixture over top of the squash. Reserve the remaining mixture in the pan. Return to the oven and bake for 30 more minutes.
Add chopped pecans into the saucepan with the remaining butter mixture, and stir to coat. Set aside. This will be your topping.
To serve, use a spatula to carefully transfer the cooked squash to a serving plate. Top with chopped pecans and sage leaves. Enjoy!