Start by adding some oil to a large pot on medium heat. Cook the onion and cucumber for about 5-7 minutes or until soft.
Add tomatoes, and cook another 5 minutes.
Add black beans and cumin, and cook about 10 minutes
Add in lemon zest and juice and chopped cilantro, stir, and let it cook another minute or so. Remove from heat.
Build your chili tacos! Layer mayo, sour cream. or plain yogurt onto a warmed tortilla. Use a slotted spoon to scoop the chili, drain it, and place it on the tortilla. Top with fresh lettuce, tomato, cheese, and hot sauce and enjoy!