Outside of Africa, substitute other greens for the Njamma-jamma leaves.
Heat oil in a large skillet or pot. Over high heat, sauté onions and garlic for a few minutes. Add cayenne pepper and stir for a minute. Reduce heat.
Add greens to pot. Cook over medium heat for several minutes. Stir greens often, but otherwise keep the pot covered.
Add water or broth. Cover. Cook over low heat until greens are tender — 10 to 20 minutes or longer. Add salt if necessary. Serve hot.