In a small saucepan, stir together quinoa and water. Bring to a boil. Cover, reduce heat to medium-low and simmer for 15 minutes, or until all liquid is absorbed and quinoa is fluffy.
Meanwhile, heat oil in a medium skillet and sauté onion and mushrooms. Cook 3 to 4 minutes, or until onion has softened. Stir in the garlic and half of the black beans, then cook for a few more minutes. Remove bean mixture from heat and place it into a food processor. Add half of the cooked quinoa, and process until smooth. If the mixture is too dry, add ½ cup water.
Transfer mixture to a bowl, and stir in remaining quinoa and black beans. Stir in flaxseeds and hot chili flakes and season with salt and pepper.
Shape bean mixture into 8 patties (about ½ cup each), and place on a baking sheet that's been greased, or lined with parchment paper. Bake for 20 minutes, or until patties are crisp on top. Flip patties with spatula, and bake for an additional 10 minutes, or until both sides are crisp and brown. Serve on a bed of arugula or with a side salad.
Per patty: 123 calories, 5 g protein, 4 g fat (2 g saturated fat), 17 g carbohydrates, 5 g fibre, 0 mg cholesterol, 176 mg sodium.