In a large skillet, heat olive oil over medium heat. Add the chopped onion and garlic, sautéing until the onion is translucent, about 5 minutes.
In a large bowl, combine the cooked lentils, cooked rice, sautéed onion and garlic, cumin, smoked paprika, salt, pepper, and parsley. Mix well to combine.
Bring a large pot of water to a boil. Carefully remove the core from the cabbage head. Blanch the cabbage leaves in boiling water for about 2-3 minutes until they are pliable. Remove and let cool.
Preheat your oven to 350°F.
Take a cabbage leaf and place about 1/4 cup of the lentil and rice mixture at the base of the leaf. Fold in the sides and roll it up tightly. Repeat with the remaining leaves and filling.
Spread 1 cup of marinara sauce on the bottom of a baking dish. Place the stuffed cabbage rolls seam-side down in the dish. Pour the remaining marinara sauce over the top.
If using, sprinkle shredded mozzarella cheese over the sauce.
Cover the dish with aluminum foil and bake for 30 minutes. Remove the foil and bake for an additional 10-15 minutes until heated through and the cheese is bubbly.