Gather all your ingredients and tools, then heat a tablespoon of olive oil in a large heavy-bottomed pot over medium heat.
Add diced onion to the pot and cook, stirring occasionally, until it becomes translucent and fragrant, about 5 minutes. You should hear a gentle sizzle and see the onions soften and turn a light golden color.
Add minced garlic to the pot and cook for another 30 seconds, until it releases a fragrant aroma. Be careful not to burn it; the garlic should become fragrant but not browned.
Place the chicken thighs into the pot, skin-side down if using skin-on, and cook until they develop a light golden sear, about 5-7 minutes per side. You’ll see the skin crisp up and the chicken turn a richer color.
Pour in the chicken broth, bringing the mixture to a gentle simmer. Use a spoon to skim off any foam or impurities that rise to the surface.
Add sliced zucchini and sprinkle in dried thyme. Cover the pot and let everything simmer gently for 20-25 minutes, until the chicken is cooked through and the vegetables are tender.
Remove the chicken thighs from the soup and set aside to rest for a few minutes. Meanwhile, add chopped spinach to the hot broth and stir until wilted, about 2 minutes. The soup should be vibrant and fragrant.
Shred the chicken meat off the bones, discarding skin and bones, then return the shredded chicken to the pot. Stir everything together to combine the flavors.
Squeeze fresh lemon juice into the soup, stirring gently to brighten the flavors. Taste and season with salt and pepper as needed.
Serve the soup hot, with a squeeze of lemon on each bowl for a fresh, zesty finish. Enjoy the comforting, low-carb goodness!