Add pasta to the instant pot along with 2 cups of water.
Add marinara sauce over pasta, do not stir.
Put the lid on your instant pot, set the vent to "sealing" and turn on high pressure for 2 minutes (see below for cooking time based on what kind of pasta you are cooking).
Allow the instant pot to come up to full pressure, cook for 2 minutes and naturally release for 4 minutes (you will see LO:04) then you can manually release the pressure.
After all pressure is gone and the pin drops, you can open the instant pot. You will notice the pasta and sauce looks watery at first. Stir well. Keep the "Stay Warm" Function stays on.
Add the frozen spinach, salt and garlic powder to the pot, stir well.
Allow the pasta to sit for 2-3 minutes to heat up the spinach.
Notes
For cooking lentil or chickpea pasta:You will need to look at the box of pasta (each size and shape will have a different cooking time).
If the box says 5-7 minutes: Cook 2 minutes high pressure, 4 minutes natural release
If the box says 7-9 minutes: Cook 3 minutes high pressure, 4 minutes natural release
If the box says 9-11 minutes: Cook 4 minutes high pressure, 4 minutes natural release
How to cook gluten freer pasta (brown rice pasta or quinoa pasta).These pastas can get gummy if overcooked in the pressure cooker. You will want to cook gluten free pasta for 0 minutes high pressure (just keep scrolling down past 1 and it will set to 0). Allow the gluten free pasta to naturally release 8 minutes before manually releasing pressure or you may notice a lot of pasta water spews from the pot.