Turn Instant Pot to saute mode. When hot add olive oil and onion. Cook until softened.
Add beef, Italian seasoning, salt/pepper, garlic powder, garlic, and red pepper flakes. Cook until browned.
Deglaze pan with about 1/2 cup of water.
Break spaghetti in half. Lay on top of meat in a criss cross pattern.Pour marinara sauce, and diced tomatoes over pasta.
Pour remaining water on top of tomatoes and down the sides. Push down with a spatula to cover pasta.
Place lid on top, and seal the valve. Cook on manual high pressure for 5 minutes.
Allow pressure to release naturally for 5 minutes. Release remaining pressure.
Stir and enjoy!