In a large skillet, saute the carrot and onions in olive oil until golden brown. Set aside 1/4 of the veggies for topping your cabbage rolls.
Combine the rest of the sauteed veggies with the cooked rice and set aside.
Remove the leaves from the defrosted cabbage head.
Cut out the tough core from each cabbage leaf.
Place the cabbage leaf in your hand and add a spoonful of the filling.
Fold over one side of the cabbage leaf, securing the filling inside and creating somewhat of a cone shape.
Push the loose leaves inside the roll. Repeat until you run out of ingredients.
Assemble the cabbage rolls next to one another in a baking dish. Cover them with the remaining sautéed veggies. (Optional: top with sauce if desired, see notes above.)