In a large skillet set over medium heat, add the sausage. Use a wooden spoon to break it up into small chunks. When the sausage is almost done, add the garlic. Saute about 2 minutes. Set aside.
Pour the crushed tomatoes, diced tomatoes, stock, celery, carrots, onions, and seasoning to the insert of a slow cooker. Add in the sausage and garlic mixture; stir to combine.
Cook on HIGH for 3 hours, or low for 6 hours.
Stir in the cubed potatoes, frozen peas and frozen corn; season with salt and pepper to taste. Cook on HIGH for 1 additional hour, or low for 2 additional hours.