Make the crust: In a large bowl, mix almond flour, oat flour, and salt. Stir in melted coconut oil (or butter), maple syrup, and vanilla. Add cold water one tablespoon at a time until a dough forms. Wrap and chill for 10–15 minutes.
Prep the filling: In another bowl, gently toss the berries and cherries with maple syrup, lemon juice, zest, and arrowroot. Set aside.
Shape and fill: Preheat the oven to 350°F (175°C). Roll out the dough and cut it into circles to fit mini tart pans or muffin tins. Press the dough into each cavity. Spoon in the fruit mixture until nearly full.
Bake: Place tarts on a baking sheet and bake for 20–25 minutes until the crust is golden and the filling is bubbling.
Cool and serve: Let tarts cool for 15 minutes before gently removing them. Garnish if desired, and serve warm or at room temperature.