Heat olive oil in inner pot on saute mode, or in a skillet over medium-high heat on stove top (see notes at end of post above). Add pepper and onion. Saute until softened, about 5 minutes. Add garlic and saute for another minute. Remove from heat and set aside.
If you have two inner pots, use a different pot than you used to saute for the next steps. If you do not have two pots, wash out the bottom of the pot you used to saute, and let it cool for at least 20 minutes.
Spray the inside of your cool, inner pot with cooking spray. Pour 1/2 cup water into bottom of pot. Place meatballs on top of water (meatballs can be frozen or fresh, this does not impact cooking time).
In a large bowl, stir together cooked vegetables, diced tomatoes, Italian seasoning, cayenne pepper, thyme, parsley, and marinara sauce.
Break noodles into halves or thirds. Spread 1/2 of the noodles over the top of the meatballs (criss cross the noodles as much as possible, you do not want them clumping). Spread 1/2 of the marinara over the noodles. Repeat with the remaining noodles and sauce.
Cook on high pressure for 8 minutes. Quick release at end of cooking time.
If you're in a time crunch and can't make the Italian Meatballs, you can also use a 24 ounce bag of frozen meatballs. I recommend the homemade though!