Cut the core from the cabbage and discard. Cut the cabbage into 4 large wedges, then set 1 wedge aside for another use. Thinly slice the remaining 3 wedges into long shreds. Set aside.
Heat the oil in a large pot or Dutch oven set over medium-high heat. Add the carrots, onions, and celery and season with 1 teaspoon of the kosher salt and ½ teaspoon of pepper. Cook, stirring, until tender, about 8 minutes.
Add the garlic and cook for 1 to 2 minutes, being careful not to burn.
Add the chicken broth, diced tomatoes, cumin, cayenne pepper, and the remaining teaspoon of salt, and ½ teaspoon of black pepper. Reduce the heat to medium and stir in the cabbage.
When the soup reaches a heavy simmer, reduce the heat to low and continue to cook for 30 to 45 minutes. The cabbage should be tender and the flavors of the soup melded.
Stir in the lemon juice. Taste and season with salt, pepper, and cayenne pepper, if needed.
Serve and enjoy!