Place a sheet pan in the oven and preheat to 425 on convection.
Peel the squash, cut in half lengthwise, scoop out and discard the seeds. Cut the squash into large, 2-3in pieces. Toss in a bowl with the roasting ingredients.
Once the oven has come to temperature, let the pan sit in there for at least 5 minutes. Add the squash to the pan and spread out evenly and roast for 25 minutes until browning develops.
Make the herb oil
While the squash roasts, add 3 tbsp of olive oil to a small pot, along with the sage, rosemary and garlic oil. Bring to a gentle sizzle, then remove from the heat and immediately add the refrigerated duck fat to drop the temperature of the oil and keep the garlic and herbs from burning. Set aside.
Plate & service
Once finished, lay the squash out on a serving platter and spoon some of the herb oil, along with pieces of the herbs and garlic, on top of the squash (only use as much as you want). Sprinkle with flake salt and serve warm.