Pat the 1 pound chicken thighs dry and cut into 2–3 inch chunks; set aside.
Turn the Instant Pot to Sauté, press Adjust and select More (Sauté More) and wait until the display reads HOT.
Add 1/4 cup vegetable or canola oil to the hot pot, wait 1 minute, then add the chicken in a single layer. Sauté 2–3 minutes, stirring a few times, until the pieces just begin to brown.
Add 1 tablespoon minced ginger, 6 cloves garlic minced, and 1/2 teaspoon red chili flakes to the pot. Stir 30–45 seconds until fragrant.
Add 6 teaspoons hoisin sauce, 6 tablespoons soy sauce, 6 tablespoons rice vinegar, 3 tablespoons brown sugar, and 1/3 cup water. Stir well, scraping the bottom of the pot to loosen any browned bits.
Cancel Sauté if it is still on, close the lid, set the steam release valve to Sealing, select the Poultry function, and set the time to 5 minutes.
When the cook time ends, allow a 10-minute Natural Release (do nothing for 10 minutes). After 10 minutes, carefully move the steam release valve to Venting to release any remaining pressure, wait until the float valve drops, then open the lid.
Gently stir the chicken to combine with the sauce, taking care not to break the pieces.
Select Sauté again. In a small bowl, whisk 2 tablespoons cornstarch with 3 tablespoons water until smooth and lump-free. Pour the slurry into the pot and stir gently.
Sauté for about 3–5 minutes, stirring occasionally, until the sauce thickens to your liking. The sauce will thicken more as it cools.
Turn off the Instant Pot and let the dish stand 5–7 minutes. Serve immediately and garnish with chopped green onions, sesame seeds, and additional red pepper flakes to taste.