Press the saute button on the instant pot.
Add diced tomatoes, tomato sauce, dried basil, italian seasoning, crushed red pepper flakes, minced garlic and salt.
Stir to combine.
Let cook for 5 minutes, stirring occasionally.
Pour in 1 cup water and deglaze the bottom of the pot.
Break the spaghetti noodles in half and place them on top of the sauce.
Pour in the remaining 3 cups water. Do not stir.
Close the lid and set the pressure release valve to sealing.
Press the manual or pressure cook button and set to 8 minutes on high pressure.
Quick release pressure.
Stir the spaghetti. It will thicken as it cools.
Serve immediately, topped with parmesan cheese.