Set the Instant Pot to sauté mode. Add olive oil and let it heat up. Add the diced onion and sauté for about 3 minutes until translucent. Stir in the minced garlic and cook for an additional 30 seconds until fragrant.
Add the chicken breasts to the pot, followed by the taco seasoning, chicken broth, and diced tomatoes. Stir to combine.
Close the lid of the Instant Pot and ensure the valve is set to sealing. Select the manual or pressure cook setting and set the timer for 15 minutes.
Once the cooking time is complete, allow the pressure to release naturally for 10 minutes, then carefully switch the valve to venting to release any remaining pressure.
Remove the chicken from the pot and shred it using two forks. Return the shredded chicken to the pot and stir in the lime juice. Season with salt and pepper to taste.
Warm the tortillas in a skillet or microwave. Fill each tortilla with the shredded chicken mixture and top with your favorite toppings.