1. Heat oil in a pan over medium heat. Add garlic; cook, stirring often, until golden, 4 minutes. Strain, reserving garlic and 3 tbsp. oil.
2. Put the 3 tbsp. oil in a large pot. Heat over medium heat. Add onion and fennel; cook until softened, about 5 minutes. Add broth, 2 cups water, the cabbage, potatoes, tomatoes, cumin, and salt. Cover and bring to a simmer; cook until potatoes are tender, about 20 minutes.
3. Top soup with fennel fronds, parsley, and garlic chips.