Make the elote ranch: Whisk together all of the ingredients until smooth. Refrigerate while you prepare the rest of the sandwich.
Make the charred corn slaw: Grill the corn over medium-high heat, turning occasionally, until lightly charred on all sides, about 8–10 minutes.
Let cool slightly, then cut the kernels from the cob.
In a large bowl, combine the corn, cabbages, red onion, jalapeño, cotija, lime juice, chili powder, smoked paprika, garlic powder, salt, and pepper.
Fold in ¾ cup of the Elote Ranch until the slaw is evenly coated. Refrigerate until ready to use.
Make the crispy chicken: Butterfly each chicken breast in half, then pound each piece to about ¼-inch thick, giving you 8 thin cutlets.
Season both sides with salt and pepper. Place the flour in one shallow bowl. In a second bowl, whisk together the eggs and milk. In a third bowl, combine the panko, garlic powder, and smoked paprika.
Dredge each cutlet in the flour, then the egg mixture, then the seasoned panko, pressing gently so the breadcrumbs adhere.
Heat about ¼ inch of oil in a large skillet over medium heat. Fry the chicken for 3–4 minutes per side until golden brown and cooked through. Transfer to a wire rack or paper towel-lined plate.
Prepare the sandwiches: Butter the sourdough and toast in a skillet until both sides are golden and crisp.
Layer avocado slices on the bottom piece of bread. Top with crispy chicken cutlet(s). Spoon a generous amount of the charred corn slaw over the chicken. Finish with the remaining slice of toasted sourdough and serve immediately.