In a medium pan, heat the oil. Add in the ground pork and callow to cook until almost brown, breaking up and large pieces.
Season with salt, pepper and paprika. Add onion and garlic and cook until soft and the meat is not raw.
In a large bowl, combine the pork, onion and garlic with the rice and tomatoes. Mix well. Add additional salt and pepper if needed.
If you can, cover and let it sit overnight. If not, you can use it right away.
Evenly spread around one cup of tomato sauce in the bottom of the slow cooker.
Place a collard green leaf on a cutting board. Toward the top end, carefully drop 2 to 3 teaspoons of the pork mixture in the centre. Begin to roll the leaf toward the bottom and then fold in the sides. Put finished rolls in the slow cooker.
Repeat until the mixture, or leaves, are finished. If you have extra pork mixture left, you can put it around the rolls in the slow cooker or freeze it for a quick weeknight dinner. I do the latter.
Cover the rolls with the remaining one cup of tomato sauce and about a 1/2 cup of water.
Put the slow cooker on low and cook for about 5 hours, or until the leaves are very soft.