1. Combine the gelatin with 2 tablespoons water in a small microwave-safe bowl and set aside to soften, about 5 minutes.
2. Pulse the icing sugar and almond flour in a food processor into a fine powder. Add the cream cheese, lemon zest, vanilla and salt and pulse until smooth and creamy. Scrape out the mixture into a large bowl.
3. Microwave the gelatin until melted, stirring as needed, about 30 seconds. Add the gelatin to the cream cheese mixture and stir thoroughly to combine. Spread out the mixture in a 9-by-13-inch baking dish and refrigerate until set, about 1 hour.
4. Meanwhile, stem each strawberry and quarter lengthwise. Cut each quarter into 5 or 6 chunks.
5. Put the graham cracker crumbs in a shallow bowl. Scoop level tablespoons of the cheesecake and roll into balls (dampen your hands with a little water to help). Coat the bottom half of each ball in crumbs, then press the top center in with your thumb to make an indentation. Put a piece of strawberry in each. Garnish each with a mint leaf if using. Store and serve the thumbprints in mini muffin liners. (These cookies can be refrigerated in an airtight container for up to 3 days.)