Anything that doesnt have tons of salt, unsaturated fats, or mass amounts of empty carbs. So it's more upto your judgment as to what is "healthy while not becoming bland.
Healthy fast food???? Of course it's pop corn (except the movie theater version) https://www.thehealthy.com/food/eating-popcorn-healthy/
Dude you can calculate all you want, even the worst food has some nutrition. Doesn't make it healthy.
If you're in or visiting California, In-N-Out is known for using fresh ingredients. They don't sell fried food either. It's probably one of the healthiest fast food places. edit: Ok they don't sell fried food other then french fries. No fried chicken or whatever, In general...... baked potato?