Make the filling ahead:
Heat 2 tbsp. oil in a large dutch oven over medium heat. Add mushrooms, onion, carrots, garlic, stirring constantly, for 8-10 minutes or until softened. Add lentils, tomato paste, cumin, and five-spice and cook, stirring for another minute. Pour in stock and season with salt and pepper. Let mixture simmer for 2-3 minutes, until liquid is absorbed. Transfer to a bowl and let cool. Filling can be made a day ahead and stored wrapped in a refrigerator.
Assemble the cabbage:
Bring a large pot of salted water to a boil. Working in batches, cook cabbage leaves in boiling water for 5-6 minutes, until bright green and softened. Drain and let cool.
Heat oven to 350°F. Fold egg or flaxseed mixture, breadcrumbs, and parsley into the lentils mixture. Season with salt and pepper.
Grease a 9-inch springform pan with olive oil. Place a large pretty cabbage leaf, domed side down, in the center of the pan. Remove any thick ribs with a knife. Arrange the leaves, layered one on top of the other, until the entire bottom and sides of pan are covered. Let leaves hang over sides of pan by a few inches. Reserve leftover leaves for filling.
Spread ⅓ of filling into pan and top with a cabbage leaf or two to cover. Repeat with another ⅓ of filling and layer of cabbage leaves. Finish with remaining filling and layer of cabbage leaves. Fold in overhanging leaves toward center and seal edges.
Bake for 45-50 minutes or until firm. Let cool for 10 minutes before unmolding. Invert a large plate or platter over the pan, and flip to unmold. Cut into slicers to serve.