Preheat oven to 450°F. Ready a baking sheet lined with foil and fitted with a wire rack. Use cooking spray to lightly spray the surface of the wire rack. Set aside.
Using a sharp knife, slice each chicken breast in half lengthwise. Next, cut each half, depending on how large they are, into 2 or 3 pieces. Use the flat side of a meat mallet to GENTLY round out the pieces. DO NOT POUND THEM THINNER THAN 1/2-INCH.
To a large zip-top plastic bag, combine the yogurt, the hot sauce ** see notes, salt, pepper, and 2 tablespoons of tap water. Seal bag and shake well to combine. Use a small whisk if necessary.
Rinse and pat dry each piece of chicken. Add to the yogurt marinade and seal. Pop into the fridge while preparing the breading.
In a shallow bowl, combine the panko with the paprika, the garlic salt, and the chili powder and mix until well combined. Remove chicken from the marinade one piece at a time and dredge in the panko mixture. Press to coat if necessary, and place onto the wire rack. Repeat with each piece of chicken.
Allow the cutlets to stand at room temperature undisturbed for at least 15 minutes and up to 25 minutes before placing into the oven. Bake for 12 minutes, then flip and bake for 15 minutes more. Cutlets are fully cooked when they register 165°F.
During the last 5 minutes of the bake, place the Brioche tops and bottoms on the edges of the wire rack to lightly toast. Be careful so as not to burn.
IF BASTING - use a pastry brush to lightly brush melted butter on both sides of the fully cooked cutlets before assembling the sandwiches.