Season the chicken with the oregano, 1/2 teaspoon of the salt, and the pepper.
2. Add the olive oil to a Instant Pot. Select Sauté and adjust to Normal/Medium. When the oil is hot, add half of the chicken and cook, turning once, until browned on both sides, 4 to 8 minutes. Repeat with the remaining chicken.
3. Select Cancel. Transfer the chicken to a plate.
4. Add the onion, bell pepper, mushrooms, tomatoes, broth, tomato paste,
garlic, and remaining 1/2 teaspoon salt to the pot. Add the chicken. Lock
the lid in place.
5. Select Manual and cook on high pressure for 12 minutes. Use quick
release.
6. Transfer the chicken to a plate; cover to keep warm.
7. Select Sauté and adjust to Normal/Medium. When the sauce is
simmering, add the zucchini noodles. Cook, stirring frequently, until the
sauce is thickened, and the zucchini is crisp-tender, about 2 minutes.
8. Select Cancel. Serve, topped with parsley if desired.