Place the oil in the Instant Pot and set on Sauté. Salt and pepper the chicken pieces on both sides. Then place them skin-side-down in the Instant Pot. Sauté for 5 minutes per side, then remove from the pot. Scrape the bottom of the pot with a metal spatula to loosen any chicken skin.
Next, add the onions and garlic to the pan juices. Sauté for 1-2 minutes. Then pour in the water and use a metal spatula to thoroughly deglaze the bottom of the pot. (Any skin or debris stuck to the bottom of the pot could later result in a "burn" notice.)
Add the fresh herbs and diced tomatoes. Season with 1 1/2 teaspoons salt and stir well. Set the chicken thighs back in the pot. Then pour the orzo on top. Lock the lid into place and set the Instant Pot on Pressure Cook High for 4 minutes. (It's important that the orzo goes in last so it doesn't stick to the bottom of the pot.)
Once the timer goes off, turn off the Instant Pot and perform a Quick Release. When the steam valve button drops, it's safe to open the top. Remove all herb stems. Taste the orzo, and season with salt and pepper as needed. Stir in the fresh basil and serve.
RECIPE UPDATE: On the newer IP models, the "burn notice" is very sensitive. Make sure your rubber seal in the lid is very clean. Then be sure to scrape, deglaze, and layer the ingredients as directed to make sure the pasta cooks properly. We have changed the layering technique in this recipe to account for this, so if you watch the video, the steps may look slightly different. If a burn notice goes off, most common on the 8 quart model, cancel the cooking session, perform a quick release, and Sauté the ingredients until the pasta has cooked through.STOVETOP INSTRUCTIONS: Follow steps 1 and 2 in a large 6-8 quart saucepot, set over medium heat. Layer the ingredients as directed in step 3, then cover and bring to a boil. Boil the chicken and orzo as directed on the orzo package, usually 7-10 minutes. Taste for seasoning, and salt and pepper as needed. Then stir in the basil. If the chicken thighs are well-seared at the beginning, they should have no issue cooking through.You can also use boneless skinless chicken thighs if desired.