Place the chicken breasts on a cutting board. Use a sharp knife to slice the chicken breast halves horizontally, butterflying them open. Cut each breast in half, to create 4 equal size pieces.
In a medium shallow bowl or baking dish, combine the flour, garlic powder, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Set aside.
In a separate medium bowl or baking dish, whisk the eggs and set aside.
In a third medium shallow bowl or baking dish, combine the panko and Parmesan cheese.
Dredge the chicken breasts in the flour mixture, coating both sides, shaking off excess. Next, dip the chicken into the eggs, letting any excess drain off. Add the chicken to the panko mixture and press until both sides are well coated. Repeat until all pieces are all breaded.
In a large cast iron skillet, heat the oil over medium high heat. Once the oil is hot, carefully place 1 or 2 pieces of chicken into the pan and cook for 2 to 3 minutes, on each side, or until chicken is cooked through.
Remove the chicken to a paper towel lined plate and repeat the process with the remaining chicken. Add more oil, if necessary.
To make the lemon dressing, combine the Greek yogurt, lemon juice, mustard, honey, garlic, salt, and pepper in a small bowl or jar. Whisk until smooth. Set aside.
Preheat the broiler. Use a serrated knife to cut the croissants in half lengthwise. Place the croissants on a large baking sheet. Brush the insides and top exterior with melted butter. Sprinkle 1/4 cup of the Parmesan cheese evenly on the tops of the croissants. Broil until slightly toasted and Parmesan cheese is melted. This will only take 1 to 2 minutes, so don’t walk away. Remove from the oven.
In a medium bowl, combine the lettuce, remaining Parmesan cheese, and dressing. Use tongs to toss until lettuce is well coated.
To assemble the sandwiches, place the chicken on the bottom halves of the croissants. You may have to cut the chicken to fit the croissant. It’s ok if some chicken hangs out of the sandwich. Drizzle with hot honey, if using. Top with avocado slices, lettuce mixture, and sandwich with the Parmesan crusted croissant half. Serve immediately.