Combine water, sugar, vanilla, and lemon juice in a saucepan and bring to a simmer.

Add apple halves, cut side down. Simmer gently 8–10 minutes until tender but not mushy.

Remove apples with a slotted spoon. Keep poaching liquid warm.

Stir butter and a pinch of salt into the liquid to make a thin syrup, if using.

Plate apples, spoon syrup over them, and sprinkle granola on top.

Serve warm or room temperature. Kids eat them with spoons; adults might want a dollop of yogurt.