Heat the pot: Set a large soup pot over medium heat and add the olive oil or butter. When hot, add the onion with a pinch of salt.
Cook 3–4 minutes until softened and translucent.
Sauté the aromatics: Stir in the garlic, thyme, and oregano. Cook 30–60 seconds, just until fragrant.
Brown the mushrooms: Add the sliced mushrooms. Spread them out and let them cook without stirring for 2–3 minutes to get some color, then stir.
Continue cooking 6–8 minutes until they release their moisture and start to brown.
Add vegetables: Stir in the carrot and celery. Cook 3 minutes to soften slightly.
Build the broth: Add the soy sauce or tamari and the bay leaf. Pour in the broth and bring to a gentle boil.
Add grains or pasta (optional): If using barley or small pasta, add it now.
Reduce heat to a simmer and cook until tender. Barley usually takes 25–30 minutes; small pasta 8–12 minutes. Stir occasionally so nothing sticks.
Stir in the kale: Add the chopped kale and simmer 5–7 minutes, until tender but still bright.
If using white beans, add them now to warm through.
Finish with lemon: Stir in the lemon zest and juice. Taste and season with salt, pepper, and red pepper flakes as needed.
Serve: Ladle into bowls and top with parsley. Add grated Parmesan or a drizzle of good olive oil if you like.