Core the cabbage and place it in a large pot of boiling water for 5 minutes to soften the leaves. Drain and carefully separate 12 leaves. Trim any thick ribs.
In a mixing bowl, combine the ground beef, uncooked rice, onion, garlic, salt, pepper, and Italian seasoning. Mix until evenly blended.
Place about 1/4 cup of the beef mixture onto the center of each cabbage leaf. Fold in the sides and roll up tightly.
Pour half the crushed tomatoes into the bottom of the slow cooker. Arrange the cabbage rolls seam-side down in a single layer.
Pour the remaining crushed tomatoes over the rolls. Cover and cook on low for 6 to 7 hours until the rice is tender and the rolls are cooked through.