Heat the olive oil in a large pot over medium heat. Add the chicken pieces and cook until lightly browned on all sides, about 5 minutes. Remove the chicken to a plate and set aside.
Add the onion and garlic to the same pot. Cook for 3 minutes until the onion softens.
Stir in the sliced fennel and cook for another 3 minutes to bring out its flavor.
Return the chicken to the pot along with the potato cubes, chicken broth, thyme, salt, and pepper. Bring the mixture to a boil.
Reduce the heat to low, cover, and simmer for 25 minutes until the potatoes are tender and the chicken is cooked through.
Remove the pot from the heat. Stir in the lemon zest and lemon juice. Taste and adjust salt if needed.
Ladle into bowls and sprinkle with fresh parsley before serving.