First, slice Little potatoes in half. Dice celery and onion. If carrots are too large, slice in half as well.
Turn Instant Pot on to sauté mode (on high.) Pour in olive oil. Once pot is super hot, add in half the stew meat. Season well with salt and pepper. Brown meat on all sides. Remove once browned and continue with the other half of the meat.
Once all the meat is browned, put all the meat back into the pot and stir in diced celery and onion. Turn off the sauté setting.
Add in the Little potatoes, carrots, beef stock, roasted tomatoes, Worcestershire sauce, minced garlic and oregano. Stir and top with a bay leaf.
Click pressure cooker lid into place.
Turn the pressure release valve to the "Seal" setting. Set to manual high pressure for 30 minutes.
Allow the pressure to naturally release for 10 minutes. Then fully vent the rest of the steam. Once all the steam is released, remove the lid. Take out the bay leaf.
In a small bowl, mix together the cornstarch and water.
Pour the cornstarch slurry into the pot and turn it onto the sauté setting on high.
Allow the mixture to simmer until thickened then turn off the sauté setting.