Set your Instant Pot to sauté mode and add olive oil. Once hot, add chopped carrots, celery, and minced garlic. Cook until the vegetables are fragrant and slightly softened, about 5 minutes, with a gentle sizzle and aroma filling the kitchen.
Add chicken breasts on top of the sautéed vegetables, then pour in the chicken broth. Sprinkle with thyme, and lock the lid onto the Instant Pot. Set to high pressure for 10 minutes, with a gentle bubbling starting to form.
Once the cooking cycle completes, carefully perform a quick release to let out the steam. Open the lid and check that the chicken is cooked through and shreddable; it should easily break apart with tongs.
Remove the chicken breasts using tongs and transfer to a cutting board. Use two forks to shred the chicken into bite-sized pieces, then set aside.
Switch the Instant Pot back to sauté mode. Let the soup simmer gently for about 10 minutes, stirring occasionally, until the broth slightly thickens and flavors meld. The vegetables should be tender and the broth fragrant.
Stir in the shredded chicken back into the pot. Zest half of the lemon and squeeze in its juice, stirring well to brighten the flavors. Taste and season with salt and pepper as needed.
Once seasoned to your liking, ladle the steaming soup into bowls. The broth should be clear and vibrant, with tender vegetables and shredded chicken visible through the surface. Serve hot, garnished with a slice of lemon if desired.
