In a pan over medium-high heat melt butter then add breadcrumbs and keep stirring constantly until breadcrumbs turn golden, will take about 3-4 minutes.
Take pan from heat and immediately place breadcrumbs on a cool plat. Mix in salt and black pepper.
Cut onion into small pieces and chop finely in a mini processor until almost liquid
Run chopped onion through a fine mesh sieve placed on top of a bowl to catch the onion juice.
Press with the back of a spoon to get all the juice out.
Beat egg, salt and pepper into the onion juice.
Add flour and mix to form a paste like mixture.
Pour mixture over chicken tenders and toss to cover.
Preheat air fryer to 400F.
Place chicken tender, one at a time, on the panko breadcrumbs.
Spoon bread crumbs over the top of the chicken tender and press to make it stick.
Place breaded chicken on your air fryer basket, spray both sides with some cooking oil and air fry for 5-6 minutes each side or until chicken is cooked thoroughly.