Gather your ingredients and equipment — you'll need a large heavy-bottomed pot, measuring tools, and your knife and cutting board.
Heat the olive oil in the pot over medium heat until it shimmers and begins to smell fragrant, about 1 minute.
Add the diced onion to the pot and sauté until it becomes translucent and soft, about 5 minutes. You should hear a gentle sizzle and see the onion turn a light golden color.
Stir in the minced garlic and cook for another 30 seconds until fragrant, making sure it doesn't brown too much.
Add the sliced chicken breasts to the pot and cook until they develop a light golden color, about 7 minutes, stirring occasionally. The chicken should be mostly cooked through and tender.
Pour in the chicken broth, bringing the mixture to a gentle simmer. Reduce the heat slightly and let it bubble softly for about 10 minutes, allowing flavors to meld and chicken to finish cooking.
While the soup simmers, zest both lemons with a microplane or fine grater, then juice them, measuring out about 2 tablespoons of lemon juice.
Stir the lemon juice, lemon zest, chopped parsley, and thyme into the broth. Let everything simmer together for another 5 minutes, enhancing the bright, citrusy aroma.
Taste the soup and season with salt and freshly ground pepper as needed, balancing the flavors.
Turn off the heat and let the soup rest for a few minutes, allowing the flavors to settle and develop further.
Serve your lemon chicken soup hot, garnished with extra parsley if desired, and enjoy the lively, comforting flavors of this bright broth.
