Warm the oil in a large pot over medium heat. Add the onion, carrot, celery and ¼ teaspoon of the salt. Cook until the veggies are tender, stirring often, about 5 to 8 minutes.
Add the garlic, oregano, and another ¼ teaspoon salt. Cook until fragrant while stirring constantly, about 1 minute.
Increase the heat to medium-high and add the cabbage. Cook for 5 minutes, while stirring frequently.
Pour in the water and tomatoes (add 1 more cup of water if you want a more brothy soup). Bring the mixture to a simmer and cook, uncovered, until the veggies are nicely tender, about 15 minutes.
Remove the pot from the heat and stir in the fresh herbs, 1 tablespoon lemon juice or vinegar, and about 10 twists of freshly ground pepper. Taste, and adjust as necessary—add up to 1 more tablespoon lemon juice or vinegar for more zing, another ¼ teaspoon salt for more overall flavor, or more black pepper. Serve in bowls. Leftovers keep well in the refrigerator for up to 5 days, or in the freezer for up to 6 months.
