1. In a large bowl, toss onion with vinegar; let stand 10 minutes. In another bowl, use a fork to combine goat cheese, lemon zest, salt and pepper.
2. Remove onion from vinegar, shaking off excess, and transfer to a small plate. Whisk honey and oil into vinegar, add frisee, and toss to coat.
3. Divide goat cheese mixture among 4 slices of bread. Top with apple, onion, frisee, dill and remaining bread.