Put Instant Pot on Saute setting, put in the oil and cook coarsely chopped onion until it becomes transparent (stir frequently)

Add the tomato, green chili, and taco seasoning

Place the chicken breasts in the pot, (no need to thaw them first)

Set lid for pressure and place on the pot

Use poultry setting for 30 minutes.

Use quick release on pressure when cooking is completed

Remove chicken breasts and shred them, replacing the shredded chicken back into the pot

Put Instant Pot on warm for serving