Slice the onions into half-moons.
In a small bowl, whisk the lemon juice, red wine vinegar, minced garlic and oregano.
Place the chicken breasts in the Instant Pot insert and sprinkle the onions around them. Season with a few pinches of salt and pepper. Pour the lemon juice mixture over the top. Add in 1/2 cup hot water.
Cook on High, Manual mode for 15 minutes, or until chicken is cooked through.
Let naturally release for at least 10 minutes.
Once cooked, shred the chicken with the sauce and keep on warm mode until ready to serve. Strain before adding to the pita or naan bread.
Prepare the garnish and tzatziki sauce.
Serve Instant Pot Chicken Gyros on pita or naan, with red onion and/or cucumber garnish and tzatziki sauce.
Slow Cooker Directions:Place the chicken breasts in the base of the slow cooker and sprinkle the onions around them. Season with a few pinches of salt and pepper. Pour the lemon juice mixture over the top. Set on low and cook for 8 hours. Once cooked, shred the chicken with the sauce. Strain before adding to the pita or naan bread.