Preheat the oven to 175°C (350°F) and place a rack in the center.
In a large bowl, combine the oats, almond flakes, hazelnuts, melted coconut oil, maple syrup, and a pinch of sea salt. Mix until everything is evenly coated.
Lightly grease four 5-inch mini tart tins. Divide the mixture evenly between them, using about 3 tablespoons for each, and press it firmly into the base and sides with your hands.
Bake for about 15 minutes, or until the tart shells are golden and crisp. Remove from the oven and gently press the center of each tart with the back of a spoon to reshape them if they have puffed up. Set aside to cool completely.
Meanwhile, prepare the mascarpone cream by mixing the mascarpone and sugar in a bowl until smooth and creamy. Add the orange zest and stir until just combined. Refrigerate until needed.
Once the tart shells are completely cool, carefully remove them from the tins using a small knife if necessary, handling them gently as the crust is delicate.
Fill each tart with 2–3 tablespoons of mascarpone cream, then top with fresh blueberries, a sprinkle of freeze-dried strawberries, and a few mint leaves.
Serve immediately, or store in an airtight container in the refrigerator for up to 2 days.