Place the whole chicken in a large stockpot and cover with cold water. Bring to a gentle simmer over medium heat, skimming off any foam that rises to the surface for the first 15 minutes.
Add the diced onion, sliced carrots, chopped celery, fresh thyme sprigs, and a pinch of salt. Stir gently and let everything simmer uncovered on low heat for about 1.5 to 2 hours, until the chicken is tender and falling apart.
Carefully remove the chicken from the broth and set aside to cool slightly. Strain the broth through a fine-mesh strainer into another pot, discarding the solids. Return the clear broth to the stove and keep it at a gentle simmer.
While the broth simmers, pick the tender meat off the chicken bones, shredding it into bite-sized pieces. Discard the bones and skin.
Add the shredded chicken back into the simmering broth, along with the chopped parsley and a squeeze of lemon juice. Taste and adjust seasoning with salt and pepper as needed.
If desired, cook noodles or rice separately according to package instructions and add to each bowl when serving for a heartier meal.
Serve the hot soup garnished with additional fresh herbs and a wedge of lemon for brightness. Enjoy the comforting aroma and tender, flavorful broth.