Have ready a crock pot, or saucepan in which to cook the chili.
Peel the sweet potato and cook it in a dish with a small amount of water, until soft. This is easily done in the microwave by cooking, covered for about 8 minutes.
Mash the sweet potato.
Put the crushed tomato, tomato paste, and mashed sweet potato in the cooking pot and mix.
Drain the beans and add to the pot
Chop the pepper(s) and add to the pot
Crush/chop the garlic and add to the mixture
Chop the onion, celery and oregano(optional), and add to the mixture
Sprinkle the cumin over the mixture and stir well
Crumble the tempeh and add to the mixture
Heat the pot until small bubbles start to break the surface. Immediately reduce the heat and let it simmer for about 2 hours.
Then it is ready to serve, or can be left keeping warm for a little while to allow time for the flavor to develop.