Mix mascarpone, honey, lemon juice, cinnamon, and salt in a bowl until smooth. Taste and add more honey if you like it sweeter.

Toast bread in a skillet with butter or under the broiler until golden. Watch closely—toast burns faster than you think.

Spread a thick layer of mascarpone on each toast. Arrange apple slices on top in a single layer.

Drizzle with a little honey and sprinkle walnuts or mint if using. Serve right away.