Bring a pot of salted water to a boil. Cook the corn until tender. Drain well, then cut the corn kernels from the cobb.
Make the corn salad: Transfer the kernels to a medium-sized mixing bowl. Prep the other ingredients per instruction above and add to the bowl. Mix well. Stir in crumbled feta. Set the bowl aside to marinate while you prepare the beans and guacamole.
Warm the olive oil in a large saucepan over medium heat.
Prep onion per instruction above. Add the onion to the pan and cook, stirring occasionally, until the onions have softened. Add the cumin and cook for about 30 seconds while stirring. Add the beans and water. Stir, cover, and reduce heat to simmer for 5 minutes. While simmering, make the guacamole.
Make the guacamole: Slice the avocados in half, remove the pit and skin, then place in a mixing bowl. Mash the avocado with a fork. Add the remaining ingredients (except the chips) and stir them together. Season with salt and pepper to taste.
Finish the beans: Use the back of a fork to mash up at least half of the beans. Remove from heat and season generously with salt and pepper to taste. Cover with lid to keep warm until you’re ready to serve.
Warm the tortillas: Heat a cast iron or non-stick skillet over medium heat and warm each tortilla individually, flipping occasionally.
Prep the avocado for the tacos per instruction above.
Assemble the tacos: Spread black beans down the middle of each tortilla. Top the beans with corn salad. Place a slice of avocado on the side of the beans.
Margarita: Mix all the ingredients for the mocktail until combined. Serve over ice.
Serve: Enjoy the tacos with optional salsa verde or hot sauce on the side, chips and guacamole, and margarita mocktail.