Bring a large pot of water to a boil. While it heats, cut the core out of the bottom of the cabbage, keeping the head whole.
Carefully submerge the whole cabbage head, cut side down, into the boiling water. Use the pot lid to keep it submerged if needed. Boil for about 12 minutes, removing leaves one by one with tongs as they loosen. Place leaves in a colander to drain and cool. You'll need about 12 large leaves. Set remaining cabbage aside.
While the cabbage cools, heat olive oil in a large Dutch oven or deep skillet over medium-high heat. Add diced onion and cook for 5 to 7 minutes until translucent. Add garlic and cook for 1 minute until fragrant. Remove from heat.
In a large bowl, combine the cooked onion and garlic with meatless ground, one 8 oz portion of tomato sauce, fresh dill, dried parsley, 1 teaspoon salt, and ½ teaspoon pepper. Mix well, then fold in cooked white rice.
Once leaves are cool enough to handle, trim the thick center vein from each leaf with a paring knife. Lay each leaf flat, inner side up.
Add about ½ cup of filling near the bottom center of each leaf. Fold the bottom up over the filling, fold in the sides, and roll upward like a burrito. Place seam side down. Repeat with remaining leaves and filling.
Roughly chop the remaining boiled cabbage and spread in a shallow layer across the bottom of your Dutch oven. Arrange stuffed rolls seam side down on top in a single layer.
In a small bowl, combine the remaining tomato sauce, diced tomatoes with their juices, water, 1 teaspoon salt, and 1 teaspoon pepper. Pour over the cabbage rolls.
Cover and bring to a boil over high heat. Once boiling, reduce to a low simmer and cook for 40 to 45 minutes, until cabbage is fully tender and rolls cut easily with a fork.
Serve with spoonfuls of the tomato and cabbage base from the bottom of the pot. Garnish with fresh dill sprigs if desired.