In a large bowl, mix all sauce ingredients and set aside.
Sauté diced onions in oil over medium heat with salt and pepper for 5-7 minutes until golden.
Add garlic and cook for 1 minute.
Let cool, then combine with vegan ground beef, rice, fennel, salt, and pepper in a bowl.
Cut a cone shape around the stem of the cabbage.
Boil a large pot of water and cook the cabbage for about 3 minutes.
Remove leaves two at a time, continuing until you have 16-18 leaves.
Preheat oven to 325°F (160°C).
Spread 1 cup of sauce in a casserole dish.
Place a cabbage leaf on a board, trim the rib, and fill with ¼ cup of the mixture.
Roll burrito-style and place seam-side down in the dish.
Cover with remaining sauce, seal with foil, and bake for 2 hours and 45 minutes.
Let sit for 10 minutes before serving.