Preheat oven to 375°f.
Using a sharp knife, remove the core from the cabbage.
In a large pot, bring enough water to a boil.to completely cover the cabbage
Reduce heat to simmer and simmer for at least half an hour (make sure cabbage is not resting on the bottom of the pan, it should be floating)
While the cabbage is simmering, in a large skillet, brown the ground beef and chopped onion.
add the salt, pepper and garlic powder and mix thoroughly.
Stir in riced cauliflower and mushroom p[ieces and combine well.
Once the cabbage is cooked, remove the outer leaves with tongs and continue to simmer until you have removed enough leaves for the recipe.
Spray the baking dish with non stick cooking spray and line with 6 cabbage leaves.
On a flat surface place a cabbage leaf and fill with 2-3 tablespoons of the ground beef mixture.
Tightly roll the cabbage roll and place, seam side down into the lined baking dish.
Repeat for the rest of the cabbage rolls.
in a small mixing bowl combine tomato sauce, lemon juice, Splenda and water and mix well.
Spread the sauce over the cabbage rolls and cover with aluminum foil.
Bake at 375°in the oven for 50 minutes