In a large pot, toss the sliced onion with the olive oil and salt. Saute over medium heat until the onion is softened and transparent.

While the onions are cooking, drain the whole plum tomatoes and reserve the juice. Dice the tomatoes.

Add the cayenne, cumin, black pepper, garlic, and diced tomatoes. Saute for five more minutes, then add the reserved tomato juice, vegetable broth, and one empty tomato can full of water.

Bring to a boil, then reduce the heat and simmer for 20 minutes.

Add the chickpeas and let them heat through before serving.