Press Sauté function on the Instant Pot and use Adjust to select “More” mode. When the word “Hot” appears, swirl in oil.
Add sausage to uncovered instant pot, cooking for 4 minutes or until browned, stirring frequently. Remove sausage from cooker.
Add in chicken to instant pot; cooking for 2 minutes on each side or until lightly browned.
Stir in 2 1⁄2 cups water and next 8 ingredients on the list to the Instant Pot (brown rice through bay leaves). Close and lock the lid of the Instant Pot.
Turn the steam release handle to “Sealing” position. Press Manual; select “High Pressure,” and use [-] or [+] to choose 18 Minutes pressure cooking time. When time is up, turn cooker off. Open the cooker using Quick Pressure Release.
Stir in sausage, Old Bay seasoning, shrimp, and tomatoes.
With lid off, press Sauté, and use Adjust to select “More” mode. When mixture comes to a boil, turn the Instant Pot off.
Press Sauté, and use Adjust to select “Normal” mode. Simmer 5 minutes or until shrimp are done, stirring frequently. Turn cooker off. Remove inner pot from cooker; let stand 15 minutes before serving.
Divide jambalaya among 8 bowls . Garnish with sliced scallions, if desired. Enjoy!