Heat 2 tablespoons oil in a large heavy-bottomed pot over medium heat and add the carrots, celery, onion, ¼ teaspoon salt, and a few grinds of pepper. Cook until softened, stirring occasionally, about 8 minutes. Add 4 minced garlic cloves, 1 teaspoon cumin, and ¼ teaspoon chili flakes. Cook until fragrant, about 30 seconds more.

Add the tomatoes, 4 cups broth, and 2 tablespoons citrus juice. Cover and bring to a boil.

Add the potatoes and chickpeas, and simmer with the lid ajar until the potatoes can be pierced easily with a fork, 30 to 40 minutes.

While the soup simmers, make the tortilla crisps (optional). Heat the oven to 350ºF. Place 1 tortilla on a cutting board and lightly brush both sides with oil. Place another tortilla on top of the greased one and brush the top with oil; continue stacking and brushing all tortillas. Slice the stack into ⅓-inch strips. Transfer to a baking sheet and arrange in a single layer. Sprinkle with salt. Bake until the tortillas are lightly brown and crispy, flipping once halfway through baking, about 15 minutes.

When the soup is ready, ladle about half into a separate container and puree the half remaining in the pot with an immersion blender (see below for upright blender instructions). Combine both halves, taste, and adjust the seasonings, if needed. (If you don’t have a blender, you can leave the soup unblended).

Serve topped with cilantro, avocado, and tortillas.