Cook the corn tortillas. Pour about ½ - 1” inch oil into the skillet and turn the stove on to medium heat. Use a thermometer to check if the oil is hot enough, about 350 degrees. As soon as the oil is at the correct temperature, use tongs to place the tortilla into the pan. Cook each tortilla for about 10 to 15 seconds. Flip it over and cook for another 10 seconds. Remove it from the oil using the tongs and place on a paper-towel-lined plate. Sprinkle with salt.
Shred chicken from rotisserie chicken or cooked poached chicken breasts. Toss with taco hot sauce and chopped chipotle chilies. Sprinkle on top of tostada shells. Top with cotija cheese and place on a baking sheet and put under the broiler to heat up.
Top with pickled red onion, fresh avocado, jalapenos, and cilantro. Serve immediately.
Thinly slice the onions (I prefer to use a mandoline). Place the sliced onions into a 16-ounce jar.
In a small pot, heat the vinegar, water, sugar, and salt over medium heat until the sugar dissolves, about 1 minute. Let cool and pour on the onions.
Place in the refrigerator to chill. The pickled onions are ready once they are a bright pink color and are tender, about 2-3 hours for thinly sliced onions. For thicker onions, you may need to refrigerate overnight.