First, prepare the Pinto beans according to the directions on the packaging. This may require an overnight soak. When cooking the beans, only cook them about halfway. You can prepare the stock as they cook.
Next, prepare the stock: Fill a large pot with 6 cups of water, and bring to a low boil. Coarsely chop Onion, and add to pot. Cut up 1 avocado into large pieces and add to pot. Cut the top off of the Habañero pepper, and add to pot. Break flounder fillet into small pieces, and add to pot. Whisk 1 tablespoons of Wasabi mustard into the pot. Add 1 tablespoons of Horseradish to pot. Finally, add the partially cooked pinto beans to the pot. Now, let the whole mixture simmer for about 1 hour.
While the stock simmers, you can prepare the base: Cut up the 2 remaining avocados and place in a blender. Add another 1 tablespoons of Wasabi mustard to the blender, along with 1/4 cup of water. Scoop out the other avocado and the Habañero pepper from the stock pot, and add to the blender. Blend these ingredients until they are fully puréed. You may need to add another 1/4 cup of water.
Now, strain the stock through a colander to remove the onion, fish pieces, and beans, but KEEP the strained liquid. That is your stock. You can discard the onions, fish, and beans, or use them in another dish. I added them to some whole grain rice for a healthy, fiber-rich side dish.
Pour the strained stock back into the large pot. Put it on medium-low heat, and gradually whisk in the avocado purée, until fully blended. Add salt and pepper to taste.
Tip: If the soup is too thin, let it simmer for a while and it will reduce and get thicker. If the soup is too thick, you can add a bit of water.