Core the cabbage with a pairing knife by making 4 incisions to cut out a pyramid-shaped piece of the thickest part of the core.
Add oil to a large sauté pan over medium heat. Add the onion and cook for 5 minutes, then stir in the garlic and cook for an additional 2 minutes.
Stir in the tomato paste, carrot, parsley, rice, lentils, Italian seasoning blend, salt, and pepper. Set the rice and lentil mixture aside.
Gently pull off 12 leaves and pat each one dry. Remove thickest part of each leaf by cutting a V-shaped portion of the leaf out (see picture below).
Add 2-3 tablespoons of filling to each leaf and roll them up (like a burrito).
Reserve ⅓ cup of sauce and pour the rest of the sauce into a 9" x 13" pan. Lay the cabbage rolls seam side down in the pan and pack them together tightly so they don’t unroll while baking. Pour the rest of the sauce over the rolls.