Preheat: the oven to 400°F. Line a rimmed baking sheet with foil — the cleanup matters — and set the wire rack on top.
Pound: the chicken to an even 3/4-inch thickness. If the thin end is already close, just bully the thick end a little. Nobody wants a dry sliver of chicken and a raw middle in the same bite.
Pat: the chicken dry with paper towels. Wet chicken doesn't hold glue; it repels it. I skipped this once and watched the coating slide off in one sad sheet.
Stir: the mayo, ranch packet, and lemon juice in the medium bowl until it's one pale beige paste. It doesn't need to be perfect, just uniform.
Spread: the mixture over both sides of each breast. Use the back of a spoon and make sure there are no bare spots. This stuff is glue, and glue only works if it touches everything.
Toss: the panko, melted butter, and parmesan together in the small bowl until every crumb looks damp. The butter is what gives you the golden crunch, so if you see dry pockets, keep tossing.
Press: the crumb mixture onto the top of each breast. Use the flats of your fingers and press firmly — but don't flatten it into a paste. You want some clumps in there. Leave the bottom of each breast bare. It feels wrong, but the bottom doesn't need crumbs because the rack is doing the work.
Bake: for 22 to 25 minutes, or until the thickest part of the largest breast reads 160°F. It'll climb to 165 while it rests. Don't skip the thermometer here — the last 5 degrees is the difference between juicy and sad.
Broil: for 90 seconds to finish. Watch it the whole time. Broilers are liars and will burn your dinner while you're looking at your phone!
Rest: for 5 minutes, then slice against the grain. Finish with chives cut on a sharp bias and set the chicken on a warm plate.