In a large, heavy-bottomed stockpot, warm the olive oil over medium-low heat. Once it's hot, add the onion, carrots, and celery. Cook until they start to soften, approximately 8 minutes.
Add in the garlic and cook until it becomes fragrant, which should take around 30 seconds. Afterward, add the zucchini and green beans, and continue cooking for an additional 4 to 5 minutes, giving it an occasional stir.
Toss in the cauliflower and cabbage leaves. Pour in the stock, turn up the heat to high, and bring it to a simmer. Once it starts simmering, season it with bouillon and cayenne.
Taste and adjust the seasoning with salt and pepper as needed.
Lower the heat to a gentle simmer, cover, and let it cook until the vegetables become easily pierced with a fork, which should take approximately 20 minutes. Then, add the spinach leaves and stir until they wilt.
Remove from heat and add the parsley and lemon juice.
Adjust seasonings. Serve hot.