Carefully remove the kernels from the corn cob and place in a bowl. Save the corn cob for making stock if desired. Cut the avocado in half, remove the pit, and scoop out the avocado onto a cutting board, cut side down. Dice the avocado into ¼” cubes and add to the bowl with sweet corn. Squeeze in the lime juice followed by the salt and cilantro. Toss until the corn and avocado are coated, set aside. Make the blacks beans as instructed. Heat the tortillas as desired (see note for my preferred method). Assemble the tacos with a a few spoonfuls of the black beans followed by the avocado relish, cotija cheese, and a drizzle of hot sauce.