Carefully peel off whole cabbage leaves, discarding any torn or discolored ones. Bring a large pot of water to a boil, then blanch the leaves for about 2 minutes until slightly tender and flexible. Drain and set aside to cool slightly.
In a skillet, heat olive oil over medium heat until it shimmers and begins to smell fragrant. Add chopped mushrooms and cook, stirring often, until browned and tender—about 5 minutes. Add minced garlic and cook for another 30 seconds until fragrant and aromatic.
Transfer the sautéed mushrooms and garlic to a mixing bowl. Add cooked quinoa, chopped walnuts, chopped parsley, smoked paprika, soy sauce, and a good pinch of salt and pepper. Mix everything thoroughly until well combined; the mixture should be moist but hold together when shaped.
Lay a blanched cabbage leaf flat on a clean surface. Spoon about 2-3 tablespoons of filling near the stem end of the leaf. Fold the sides inward, then roll tightly from bottom to top, sealing the edges with a little water if needed. Repeat with remaining leaves and filling.
Arrange the filled cabbage rolls seam-side down in a lightly oiled baking dish, snugly fitting them together. Pour the tomato sauce evenly over the rolls, covering them completely.
Cover the dish with aluminum foil and bake at 180°C (355°F) for 35-40 minutes, until the leaves are tender and the filling is heated through. The sauce should be bubbling and slightly thickened, filling the kitchen with a warm aroma.
Remove from the oven and let rest for about 5 minutes before serving. Carefully plate each roll, spooning extra tomato sauce over the top, and sprinkle with fresh herbs if desired. Enjoy the hearty, plant-based comfort!
