Saute onions and peppers in olive oil (use Instant pot on Saute or in skillet if using crock pot). cook for 3-4 minutes or until tender.
Add marinara, pesto and salt, cook together for 1 minute. Add chicken breasts to pot.
Instant Pot: cook on high pressure for 12 minutes. Manual release. Remove chicken and shred. Add mushrooms to broth and veggies in pot and cook on saute mode for 3-4 minutes. Add shredded chicken back, and simmer for 3-4 minutes.
Crock pot: Pour 1/2 cup water to pot; Add veggies mixture and mushrooms. Place chicken breasts on top and cook on low for 4-5 hours.
Top with parmesan if desired
**I served this on top of spaghetti squash which I cooked in Instant pot for 10 minutes. So easy!