Brown ground beef until no longer pink. Drain fat and mash with potato masher until no lumps remain.
Puree the diced tomatoes in a food processer or blender until smooth.
Put ground beef into slow cooker and add remaining ingredients, stirring to mix together. Cook on low for 5 and 1/2 hours. Remove cover and turn to high for remaining 1/2 hourto allow to thicken. If still too soupy, mix remaining liquid from tomatoes with corn starch to thicken. Serve on toasted hard rolls or hamburger buns.