Start by carefully slicing the chicken breast sideway. Season the chicken breasts with salt, black pepper, garlic powder, onion powder and paprika then set aside. To a small bowl, add and combine the milk, lemon juice and egg. Place both chicken breast pieces into the milky mixture and allow them to soak for 15 minutes.
While the chicken is soaking in the milk, prepare the flour breading. Add and combine all the breading ingredients to a shallow bowl. Remove the chicken breasts from the milky mixture and place them into the flour breading and ensure the chicken gets fully coated in the flour. Turn the chicken a few times in the flour to coat it as much as possible.
Place the bowl in the fridge with the chicken still in the flour. After 30 minutes, remove the chicken from the fridge and turn the breasts again to ensure they are coated well. Allow the chicken to sit at room temperature while you heat the oil in a frying pan or skillet.
Once the oil reaches 150oC/302oF, carefully place both chicken pieces into the pan. Cook for 10 - 12 turning half way through. If you have a thermometer then ensure the chicken reaches 72oC/161oF.
Remove the chicken breasts and place them on a plate lined with kitchen towel. Allow to sit for 2 minutes. Add 1 teaspoon of mayo on both sides of each brioche bun and spread. Place the chicken on the bottom buns then top the chicken with lettuce. Place the top bun on the lettuce and serve.