Add 1 cup of marinara sauce and ¼ cup of water to the bottom of a 3-quart or larger Crock Pot or ducth oven.
Stir to combine.
Set a cabbage leaf on a working surface, outer side down, and scoop about ½ cup of the mushroom-lentil mixture into the middle. Fold the stem about ⅓ of the way, then fold in the sides, like a tortilla. Continue rolling semi-tightly until completely rolled up.
Lay roll seam-side down on top of the marinara sauce.
Repeat with remaining cabbage leaves, piling each into the slow cooker in one or two layers, right on top of one another, or in the base of a dutch oven.
Add the remaining marinara sauce and 1 can of fire-roasted tomatoes.
For the crock pot, cook on high for 4-5 hours or on low for 8-10 hours.
To serve, scoop out a little marinara and spread it on a plate.
Carefully remove cabbage rolls one at a time and transfer to the plate.
Ladle an additional spoonful or two of the marinara sauce from the slow cooker over the top of each roll and top with a few sprigs of fresh dill and parsley.