To make the plum filling: In a small saucepan, combine the dried plums, water, agave syrup, and orange liqueur. Bring to a boil over high heat, then lower the heat as much as possible, cover, and simmer for 5 minutes. Remove from the heat, and let stand for 10 minutes. Sprinkle in the flour, and stir until thoroughly combined.
Preheat the oven to 350℉. Oil a 9-inch square baking pan.
To make the crust: In a medium bowl, combine the pastry flour, Sucanat, and salt, and stir until well mixed. Grate the chilled coconut oil into the flour mixture, then toss until the bits of coconut oil are evenly coated. Mix gently with your fingers, squeezing to break up the bits and working quickly so the warmth from your hands doesn't melt the coconut oil. Add the soy milk, and stir until just combined. Press a bit of the mixture in your hand to see if it holds together—if it's crumbly, stir in a bit more soy milk.
Scrape the dough into the prepared pa,n and press it in an even layer. Bake for 5 minutes. Let cool. Leave the oven on.
Meanwhile, prepare the streusel: In a medium bowl, combine the flour, oats, walnuts, Sucanat and salt, and stir until well mixed. Add the coconut oil, and stir until thoroughly combined. If any loose flour remains, stir in a bit more oil.
Spread the plum filling over the crust in an even layer. Scatter the streusel evenly over the top, and press to flatten slightly. Bake for 40-45 minutes, until the streusel is golden brown and feels firm to the touch.
Transfer the pan to a wire rack, and let cool completely. Cut 4 by 4, to make 16 squares. Stored in an airtight container in the refrigerator, the bars will keep for about 1 week.