Cook the potatoes. Let them cool slightly, then peel them and lightly mash them up with a fork; season the potatoes with salt.
While they cook, chop the onion and the lettuce and crumble or shred the cheese. Make sure everything is ready and nearby, so you can assemble these enchiladas with ease.
Pour red enchilada sauce into medium bowl; set aside.
In large skillet, heat 1/4 cup vegetable oil over medium-high heat. Carefully, lay one corn tortilla in oil, fry it for about 30 seconds, then flip the tortilla over and fry it for another 30 seconds. Using a slotted spoon, remove the tortilla from the oil, letting the excess oil drip off back into the skillet.
To prepare the red enchilada sauce, bring water and chilies to a boil in a small saucepan. Let cool slightly. Puree in blender until smooth. Strain in to bowl. Season with a couple of pinches of salt.
To prepare the tomato salsa, bring water and tomatoes to a boil in a medium sauce pan. Let cool slightly.
Puree in a blender until smooth. Pour into large bowl. Season with a couple of pinches of salt. The sauce should be a slightly thinner consistency than canned tomato sauce. If your salsa is too thick, stir in a little more water.
Dip tortilla in the red enchilada sauce, making sure to cover both sides with sauce.
Place tortilla on plate. Spoon 1 to 2 tablespoons of mashed potato and cheese onto center of tortilla. Sprinkle with desired amount of chopped onion.
Fold tortilla in half, as you would with a taco or quesadilla.
Repeat with remaining tortillas and filling. Garnish enchiladas with shredded lettuce and top with tomato salsa. Sprinkle more cheese over the enchiladas. Enjoy.