Cut onion in half, then into thin strips. Spread pieces apart.
In a medium bowl, mix honey, mustard, and vinegar. Toss well with onions (if onion is very large and the mixture isn’t coating it well, add more of each ingredient). Let it sit for 20 to 30 minutes (don’t skip this step!)
Combine flour, salt, and chili powder. Add to marinaded onion strings and toss very well.
Heat oil in a small saucepan or deep fryer. When oil is hot, deep fry onion strings in batches until golden, stirring occasionally so they don’t stick together.
Remove from fryer and drain on paper towels. Enjoy them on their own with a dip or serve over or alongside your main dish.