Turn the instant pot to the sauté function. Season chicken with 1/4 teaspoon salt and 1/8 teaspoon pepper. Once the pot is heated, add 1 tablespoon olive oil and let heat for 20 seconds. Add chicken and brown 1-2 minutes each side. Remove from pot. Add remaining tablespoon olive oil, onion and 1/4 teaspoon salt. Cook for 2 minutes. Add mushrooms, peppers and garlic, then cook for 2 minutes.
In a small bowl, whisk together tomato purée, tomato paste with the remaining salt, pepper and Italian seasoning. Return chicken to instant pot and place with vegetables. Pour in tomato mixture and gently stir to incorporate. Secure the lid. Select manual and cook on high pressure for 8 minutes.
Once cooking is complete, use the steam quick release feature. Once steam is completely released, open the lid. Gently stir mixture and serve.
Pro Tips: 1. Use a towel when pressing the quick release to avoid burning your hand. 2. For a thicker sauce, remove lid and let rest in pot for a few minutes before serving.