Heat oven to 350°F. Spray a 9-in. tart pan with removable bottom with nonstick cooking spray. Line with parchment paper; spray parchment.
In a food processor, pulse walnuts and almond flour to form fine crumbs. Add vegan butter and 2 Tbsp maple syrup and pulse to form sticky dough. Transfer dough to prepared pan and press evenly on bottom and up side. Prick with a fork and freeze 5 minutes. Bake until golden brown on edges, 9 to 11 minutes.
Meanwhile, in a small saucepan, bring beets and pomegranate juice to a simmer and cook until tender, 30 to 45 minutes.
Transfer beets and juice (should be about ¼ cup juice) to a blender. Add oat milk, molasses, orange zest and juice, vanilla, and remaining 3 Tbsp maple syrup and puree until smooth. Add agar agar and puree 30 seconds.
Transfer beet mixture to saucepan and bring to a boil. Reduce heat and simmer 2 minutes. Let cool 5 minutes, then strain into tart shell. Let stand at room temperature until cool and firm, about 1 hour. To serve, remove tart from pan and sprinkle pomegranate seeds around edges.
