Bring a large pot of water to a boil. Core the cabbage and peel away 10 to 12 large outer leaves. Blanch leaves for 2 to 3 minutes until pliable, then drain and set aside.

Cook lentils in simmering water until tender, about 20 to 25 minutes. Drain. Cook rice separately according to package directions. In a skillet, heat oil over medium heat. Sauté onion 5 minutes, add mushrooms and cook 5 to 7 minutes until browned. Stir in garlic, paprika, thyme, salt, and pepper for 1 minute. Remove from heat and fold in lentils and rice.

Whisk together crushed tomatoes, tomato paste, broth, and maple syrup. Taste and adjust salt.

Place a cabbage leaf stem end toward you, trim the thick rib if needed. Spoon about 1/3 cup filling near the bottom, fold up the bottom, tuck in sides, and roll tightly. Place seam side down. Repeat with remaining leaves.

Preheat oven to 375°F (190°C). Oil a 9x13-inch baking dish and spread a thin layer of sauce on the bottom. Arrange rolls seam side down in a single layer. Pour remaining sauce over top, cover with foil, and bake 40 to 45 minutes until bubbly and tender.

Let rest 5 minutes. Plate each roll with a generous spoonful of sauce. Top with parsley and vegan sour cream if using. Serve hot.