Grease a 8-inch tart tin with a removable bottom with coconut oil. In a food processor combine oats, buckwheat groat, almonds and process until coarsely ground. Add dates, coconut oil and maple syrup, pulse until mixture looks like wet sand.
Add peaches and lemon juice into a food processor. Puree until as smooth as possible.
Pour the peach mixture, coconut cream into a saucepan and place on the stove on low heat. When the mixture becomes warm, add the cornstarch, agar-agar and maple syrup. Stirring constantly, cook until agar and cornstarch completely dissolve. Allow to boil for approximately 30 to 60 seconds.
Strain filling mixture through a mesh sieve over a small bowl. ( you can skip this step, but straining will result in a finer texture). Pour mixture into tart and refrigerate at least 4 hours or overnight to set. Garnish and serve.