In a large pot, heat the oil over medium heat.
Sauté the onion and garlic with ½ teaspoon of sea salt until the onions are soft and fragrant, about 3-5 minutes.
Add the chopped carrots, celery, and mushrooms, and continue to sauté for another 5-10 minutes until the vegetables start to tenderize.
Stir in the remaining salt, oregano, marjoram, thyme, and pepper. Cook for another minute to toast the spices.
Add the diced tomatoes, vegetable broth, and sweet potato. Stir to combine.
Mix in the quinoa, increase the heat to high, and bring the soup to a boil.
Reduce to a simmer, cover, and cook for 25-30 minutes.
Uncover the pot and add the zucchini and chopped kale. Simmer for another 5-10 minutes or until the vegetables are tender and the quinoa is fully cooked.
Remove the pot from heat and stir in the lemon juice. Adjust salt and pepper to taste.
Divide the soup into bowls and top with grated parmigiano reggiano, if desired.