Heat the olive oil in a large pot over medium heat. Add the onions, cook for a few minutes, and then add the tempeh. Cook till the tempeh begins to brown, 5 to 8 minutes. Add the green pepper and celery and cook till they're tender, another 5 minutes. Add the garlic. Continue cooking another two minutes.
Add all of the remaining ingredients, along with half a cup of water. Reduce heat to a simmer and cook until the chili is fragrant, warm, and the flavors have come together (25 to 30 minutes). Add more water as needed, if the chili becomes too thick. Serve, sprinkled with green onion or scallions.