Add in the pasta, marinara sauce, Italian seasoning, 4 cups of water, and meatballs. Stir to combine, being sure that all the pasta is fully submerged.
Secure the pressure cooker lid onto the Ninja Foodi and set the nozzle to 'seal'.
Cook on manual high pressure for 6 minutes.
Quick-release when it is done cooking. This needs to be done immediately so that your pasta does not turn to mush.
Remove the lid carefully, and stir up the pasta.
Add a layer of shredded mozzarella cheese.
Move the function of the Ninja to BAKE at 350°F for 3-4 minutes, until the cheese is browned on top.
Carefully remove and serve.
Notes
As a general rule, you look at the box of pasta you are using and cook it for 1/2 the cook time listed on the box. The pasta I used was to be cooked in 12 minutes, so I cooked for 6.