1. Put the rack that came with your Instant Pot in the bottom of the stainless steel insert. Pour 1 cup water over it, and set spaghetti squash (whole) on top of the rack.
2. Quick instructions for the Instant Pot veterans: Cook at high pressure for 20 minutes. Then, quick release the pressure, and skip to step 5.
3. If you’re new to the Instant Pot, here are step-by-step pressure cooking instructions: Close and lock the lid. Turn the pressure knob to the “Sealing” position. Press the Manual button once. You’ll see the display light up to indicate high pressure 30 minutes. Press the – button until it reaches 20. Wait 5 seconds, and the pot will beep and the display will say ON. This means it’s heating up and building up pressure, which takes about 11 minutes. Once full pressure is reached, the display will switch and start counting down the cooking time (20 minutes). Update: If you bought your Instant Pot in 2018 or later, they updated their display panel. The “manual” button is now called “pressure cook”.
4. The Instant Pot will beep when the 20 minutes are up. Click the “Cancel” button to turn off the pot. Then carefully turn the pressure knob to the “Venting” position. Be careful – when you do this, hot steam is going to come out of that knob. Just be sure to keep your hands and body clear, and turn the knob just slightly at first. As more pressure is released, you can turn it completely into the venting position, and you’ll feel the knob lift up. Once all the steam is released, you can open the pot. A safety measure on the pot is that the lid is pretty much impossible to turn, when it’s still under pressure.
5. Use hot pads to lift the squash out of the pot and set it on a cutting board. Cut it in half, and let it start to cool off. (Tip: If you cut the squash horizontally across the middle, instead of lengthwise, you’ll get longer noodles.)
6. Remove the rack and empty the water. Put the stainless steel insert back into pot.
7. Now it’s time to make the sauce in the Instant Pot. Pour the apple juice into the stainless steel insert, and click the “Sauté” button. The display will again light up saying 30 and beneath it the “Normal” light will be lit. Click the “Adjust” button until the display switches from “Normal” to “More.” Wait a few seconds, and the main display  will switch to “On”. Within a few minutes, the juice will start simmering. Let it simmer for about 3 minutes to reduce the liquid and concentrate the flavor. Then add the duck fat and stir until melted. Click the “Cancel” button to turn off the Instant Pot. Update: If you bought your Instant Pot in 2018 or later, just click the sauté button repeatedly to switch from “normal” to “more” (the “adjust” button has been removed in newer models). 
8. Scoop out the seeds from the spaghetti squash and throw them away. Then, use a fork to scrape the spaghetti squash noodles into the pot. Season generously with sea salt, and toss to coat evenly with the glaze. Taste, and add more salt if needed.

Don’t Have An Instant Pot? Here’s the Oven-Stovetop Method

1. Preheat oven to 375 degrees. With a small sharp knife, prick the whole squash all over. Place in a 9×13 pan and roast 45 minutes. Turn over and roast another 30-45 minutes, until tender when pierced with fork. Use hot pads to transfer squash to cutting board and cut in half. When cool enough to handle, scoop out the seeds and throw them away. Then, use a fork to scrape the spaghetti squash noodles into a large bowl.
2. In a small saucepan, bring juice to a simmer over medium-high heat & simmer about 5 minutes to reduce and concentrate flavor. Add duck fat and stir to blend. Remove from heat and pour over the cooked squash. Season generously with sea salt, and toss to coat evenly with the glaze. Taste, and add more salt if needed.