Warm the pot: Heat olive oil and butter in a large soup pot over medium heat until shimmering.
Sauté aromatics: Add onion, celery, and a pinch of salt. Cook 4–5 minutes, stirring, until softened. Add minced garlic and cook 30 seconds until fragrant.
Add low-carb veggies: Stir in cauliflower florets and zucchini.
Cook 3–4 minutes to get a bit of color. This builds flavor.
Season well: Add salt, pepper, thyme, oregano, and the bay leaf. Stir to coat the vegetables evenly.
Pour in the broth: Add the chicken broth and bring to a gentle boil.
Add the chicken: Stir in the chicken pieces.
Reduce heat to a simmer and cook 12–15 minutes, or until the chicken is cooked through and the cauliflower is tender.
Finish with greens and acid: Turn off the heat. Stir in the spinach until wilted. Add lemon juice.
Taste and adjust salt and pepper.
Garnish and serve: Remove the bay leaf. Sprinkle with parsley and a pinch of red pepper flakes if you like heat. Serve hot.