Rice and "Meat" stuffed Cabbage

This recipe came out of craving I had for Stuffed Cabbage. My favorite is the same as listed here which is similar (if not the same) as what I have in a Betty Crocker cookbook.

When I made this for Potokar... I couldn't find the "sauce" recipe. (I was too impatient with my phone!) The one I came up with from memory - I didn't like! (Potokar did though and even had seconds!) However, I am putting the sauce, that I do like, here.

Also I used a multi-grain rice from Minute Rice. Minute® Multi-Grain Medley It gave the filling a more "meatier" look!

2 cups cooked rice
1 cup chopped walnuts
2 peeled carrots (chopped fine) - I used purple carrots
1 pkg (10 - 12 oz) baby bella mushrooms (chopped fine)
1/2 onion chopped (or 1 - 2 tsp of onion powder)
2-3 cloves garlic minced (or 1 - 2 tsp of garlic granules/powder)
Salt/Pepper to taste (approximately 1 1/2 tsp of salt / 1/2 tsp pepper)
3 cups dark greens of choice (spinach, kale, chard) chopped
1 large head of green cabbage
1 can (15oz) of tomato sauce
1 tsp of sugar
1/2 - 1 tsp of lemon juice
1 tbls cornstarch
1 tbls water

1. Cut the core out of the cabbage. Go in at an angle - make it kind of wide as the less hard "stem" or "rib" the easier it is later.
2. Place cored cabbage in large pot. Fill with water - I like to let the water pour into the hollowed out core to loosen the cabbage. Set over high heat and bring to a boil. Roll the head around through out cooking.
3. While the cabbage is boiling, combine walnuts, cooked rice, carrots, mushrooms, onion, garlic, salt and pepper in a medium bowl and mix well. I had put the walnuts and mushrooms in a food processor and pulsed until chopped fine (but not soup.) They were pretty wet. If you find hand chopping leaves them dry - add a tablespoon or two of water.
4. Pre-heat oven to 350 degrees
5. About 15 to 20 minutes of boiling - the cabbage should start being able to be removed from the head. Using tongs, pull a leaf or two off and set on flat surface. (I usually try to separate as many as I can but leave them in the water to continue to soften as well as letting the center of the head get more pliable.)
6. Using the recently removed cabbage leaf, on the thicker end place approximate 1/4 to 1/3 cup of "meat" (Walnut/Mushroom mix) to the bottom center. Then fold the edges inward and roll like a burrito. Place seam side down in a casserole dish, roasting pan or cake pan.
7. Repeat step 5 and 6 until mix is used up.
8. Mix the tomato sauce, sugar and lemon juice in a small bowl. Pour over cabbage rolls evenly.
9. Place dish in oven for 20 - 25 minutes when the juices are boiling.
10. Mix cornstarch with water. 
11. When baking is complete - carefully pour "most" of the juices into a heat proof bowl or glass measuring cup. Add cornstarch water and mix thoroughly. Pour mix over cabbage rolls again.
12. Serve with a light cool salad.

Enjoy! Let me know what you think. Would love to hear your feedback!