Preheat the oven to 350 degrees and prepare ingredients by chopping vegetables and cooking brown rice according to the package instructions.
Heat olive oil in a large skillet over medium heat and cook the onions until golden, about 10 min. Add garlic, mushrooms, carrot, green onion, and seasonings. Cook until the veggies are tender, about 8 – 10 minutes. Stir in the brown rice and 1/2 cup of tomato sauce, then remove from heat. Coat the bottom of a 9 x 13 baking dish with a thin layer of tomato sauce.
Core a head of cabbage and bring to a boil in a large pot, until the cabbage leaves start to come apart. Fill each cabbage leaf with 2 – 4 tablespoons of the rice and vegetable mixture (depending on the size of the cabbage leaves), then roll the leaf up like a burrito, tucking in each end. Continue filling the leaves until there is no more mixture left, line the filled and rolled cabbage leaves in the baking tray.
Cover with the remaining tomato sauce and cook for 45 minutes. Makes about 5 servings.