Season chicken with chili powder, cumin, salt, and pepper.
Set Instant Pot to SAUTÉ mode and add olive oil. Sear chicken on both sides, then remove and set aside.
Add water to Instant Pot, scrape up any bits, then return chicken to pot with 1/2 cup enchilada sauce.
Cook chicken on manual high pressure for 8 minutes, then quick release and check for doneness.
Shred chicken and reduce sauce in Instant Pot if needed.
Warm tortillas in the oven, then keep them covered to stay pliable.
Mix shredded chicken and the sauce in the Instant Pot with half of the green onions, the Greek yogurt, and half of the cheese.
Spread 1/2 cup enchilada sauce in baking dish, fill tortillas with chicken mixture, roll and place seam-side down in dish.
Top enchiladas with remaining sauce and cheese, then bake until cheese is bubbly.
Garnish with remaining green onions and serve with optional toppings.