Preheat the oven to 250°F. Butterfly the chicken breasts and spread each cut piece of chicken out on a clean work surface. Cover the chicken with plastic wrap and pound each piece evenly with a meat tenderizer.
Remove the plastic wrap and place a small bowl upside down on top of each piece of tenderized chicken breast. Trace the bowl with a knife so that you're left with circular pieces and set the excess pieces of chicken breast aside for later.
Hang the circular pieces of chicken on the oven rack and bake them at 250°F for 20 minutes. Once they've baked, remove the pieces of chicken from the oven and let them cool for about 15 minutes.
Heat a pot filled with cooking oil. For the breading station, mix together the flour and spices in one bowl and whisk the eggs together with water or milk in another. Dredge the chicken chalupas in egg wash and coat them in the breading. Cut the leftover pieces of chicken into small pieces, dredge them in egg wash, and coat them in the breading as well.
Fry the chicken chalupas in hot cooking oil until golden brown and crispy, then place them on some paper towels to absorb the excess oil. For the chicken tenders, fry the small pieces of chicken until golden brown. Once they've cooled slightly, place the chalupas in a muffin pan that's positioned upside down on your work surface.
Stir together all of the ingredients for the avocado lime sauce, then spoon the sauce into the chicken chalupas. Top the chicken chalupas off with shredded lettuce, diced tomatoes, chicken tenders, diced avocado, and shredded cheddar cheese. Drizzle plain yogurt or sour cream on top to serve.
