01 - In a mixing bowl, whisk together the lemon juice, lemon zest, olive oil, minced garlic, salt, and black pepper until well combined.
02 - Place the chicken breasts in a resealable plastic bag or shallow dish. Pour the marinade over the chicken, seal, and refrigerate for at least 30 minutes, or up to 2 hours for deeper flavor penetration.
03 - Arrange three shallow dishes: combine the flour, cornstarch, paprika, cayenne, and garlic powder in the first; whisk the eggs and milk together in the second; toss the panko breadcrumbs with melted butter and lemon zest in the third.
04 - If baking, preheat the oven to 400°F and set a wire rack over a lined baking sheet. If pan-frying, heat 1/2 inch of vegetable oil in a large skillet over medium-high heat until it reaches 350°F.
05 - Remove the chicken from the marinade and pat dry thoroughly with paper towels. Dredge each breast in the flour mixture, shaking off excess. Dip into the egg wash, then press firmly into the panko coating on all sides until fully covered.
06 - For pan-frying, cook each piece 3 to 5 minutes per side until deep golden brown and the internal temperature reaches 165°F. Transfer to a paper towel-lined plate. For baking, place the coated chicken on the wire rack, spray lightly with oil, and bake 20 to 25 minutes, flipping halfway through, until crisp and cooked through.
07 - Allow the chicken to rest for 5 minutes before slicing. Garnish with fresh lemon wedges and chopped parsley. Serve immediately.