First, make the guacamole. In a bowl, mash together the avocado, lime juice, and a pinch of salt and pepper. Put it in the fridge to use it later.
Next, make the cheese sauce. Add all of the ingredients for the cheese sauce into a high powered blender. Start the blender on low, and then gradually turn up the speed. Blend it on high for about 60 seconds, until it is very smooth and creamy.
Pour the cheese sauce into a small sauce pan and put it on the stove over low heat. Stir it occasionally so it doesn't burn on the bottom. It will thicken a bit while it cooks, so it is important to whisk a few times. Let it cook for 7-8 minutes while you cook the beans.
While the cheese sauce heats up, preheat a skillet over medium heat and add 1 tbsp of olive oil to the pan. Drain and rinse the black beans, then add them to the skillet. Then add the chopped green onions, and season with a pinch of salt and pepper, as well as the chili powder and garlic powder. Use a wooden spoon to stir it together, letting it cook for 3-4 minutes, or just long enough for the onions to get slightly soft. Then remove the pan from the heat and set aside.
It is time to assemble. So get a platter or large plate, and put half of the chips in an even layer on top of the platter. Then spoon half of the black beans all over the chips, again in an even layer. Sprinkle half of the tomatoes over the top, then spoon your desired amount of cheese sauce over that.
Repeat that process again to make another layer. Chip, beans, tomatoes, cheese sauce.
Put a big dollop of sour cream and guacamole on top. Then sprinkle chopped cilantro over the whole thing to finish it off.