Place peanut butter in a microwaveable bowl; microwave (HIGH) 30 seconds. Whisk soy sauce into peanut butter until well combined. Whisk in lemon juice until well combined. Whisk in brown sugar, garlic powder and cayenne until well combined. Set aside.
Slice chicken breasts about ½-inch thick, starting with the long side. Place in a 1-gallon recloseable food storage bag. Pour half of peanut butter mixture over chicken; reserve remaining mixture.
Seal bag and toss chicken until well coated. Place bag in a dish and refrigerated at least 2 hours or overnight, rotating several times.
Weave 1-2 strips of chicken onto skewers, leaving enough room for a handle.
Prepare grill to medium heat or broiler to high. Grill or broil chicken skewers about 3-5 minutes per side or until internal temperature reaches 170°F on an instant read thermometer.
Meanwhile, reheat remaining peanut sauce in microwave, just until warm, whisking several times (about 1 minute). Serve chicken skewers with warmed peanut sauce.