Place onions and garlic into a large food processor and process until finely chopped but not liquefied.
Place the meat in the bowl of a good Stand Mixer. Add the onions and garlic. Use your stand mixer with the paddle, paddle the living daylights out of the meat with the spices until it's a sticky mess. Don't skip this step, otherwise, you will have a hamburger with seasonings, not a smooth gyro loaf.
Place 2 cups of water in the bottom of an Instant Pot. Place a steamer basket on top of it.
Lay out a sheet of foil and on top of it, make one or two meatloaf shapes out of your meat, each no thicker than 4-5 inches. If you do one big one, you will have to adjust the time accordingly. If your Instant Pot won't hold both, you could always cook one in the Instant Pot and another in the oven and see which one your family likes better (350F for 60 minutes or until internal temp of 175-180). Put this sheet of foil+ meatloaf on top of the steamer basket, leaving enough space on the sides for the steam to circulate.
Set your Instant Pot for 15 minutes at High Pressure and let it release pressure naturally.
When you open it, try not to despair at those big, gray, lumps.
Take out the two and cover them with foil and then place something heavy on it to compress it. I put a cast iron skillet on top and then carefully placed 3 cans of beans on top of the skillet to compress it.
Let it rest for 30 minutes and then slice into thin slices.
Instant Pot Gyro Recipe https://twosleevers.com/instant-pot-gyro-recipe/