Heat honey in a small non-stick pan over medium heat. Add oat flakes and stir frequently for 2-3 minutes until lightly caramelized. Add a pinch of cinnamon if desired.
Wash the apple, remove the core, and grate coarsely with the peel.
Transfer the grated apple to a bowl and immediately mix with some lemon juice to prevent browning.
Wash and halve the grapes, then add to the apple mixture.