1. Preheat oven to 375°F or 190°C. Roughly chop the onion, mushrooms, red pepper, and carrot. Add them to the blender and pulse until it becomes a chunky slurry.
3. Meanwhile, in a food processor, pulse the lentils, oats, flax, bread crumbs, tomato paste, maple syrup, mustard, and parsley. Add lentil mixture to the vegetable slurry and combine to form a "dough."