To make the sopes:
Heat about ½” of vegetable oil in a heavy duty skillet over medium heat.
In a bowl, combine the masa harina, salt and water. Use your hands to fully combine. If the dough is not coming together, add more water, 1 teaspoon at a time.
Divide the mixture into fourths. Working with one section at a time, and keeping the remaining dough covered with plastic wrap, cut the one section into 6 equal portions and form into balls. Lay a piece of waxed paper on a work surface, and place the balls of dough on the paper. Cut another piece of waxed paper and put it over the top of the dough. Use the bottom of a cup to flatten each ball into a disc about 3 inches across and 1/4” – 1/2” thick. Remove the top piece of waxed paper, and using your fingers, make a small lip on the edges of the discs. Carefully transfer the discs to the hot oil and cook for about 1 minute on each side. Remove to a paper towel lined plate to drain. Repeat with the remaining dough.
Meanwhile, make the Avocado Cream: Remove the pits and from the avocados. Use a spoon to remove the flesh of the avocado from the skin, then dice. Place in a food processor or blender. Add the cilantro, lime juice and sour cream. Process until smooth. Season to taste with salt.
To assemble the sopes: Heat up the refried beans over low heat. Take a sope, top it with about 2 teaspoons of refried beans. Add some of the chicken, lettuce and tomatoes. Top the whole thing off with the Avocado Cream.