Tip:To adapt a slow-cooker recipe to a conventional oven, follow these guidelines: add more liquid, to accommodate for greater evaporation; bring the dish to a boil over high heat in a Dutch oven, then cover the pot and put in a 350°F oven. Plan on the dish taking roughly half the time to cook in the oven as it would in the slow cooker.
Lay the ribs—bone side visible—against the sides of the slow cooker insert, lining it.
Add the remaining ingredients (except the mango) to a medium-size saucepan, stir well, and heat over high. Bring to a boil, and boil for about 15 minutes, gently mashing the tomatoes with a potato masher, until the sauce is reduced to about 2-1⁄2 cups. Pour over the ribs to cover. Cover and cook on low until tender, 6 to 8 hours.
Carefully transfer the ribs to a large serving platter and cover with foil. Let the sauce sit in the slow cooker for about 5 minutes, then use a large spoon or ladle to skim the fat off the surface. Pour the sauce into a medium-size saucepan, and bring it to a boil over high heat. Cook until reduced to about 1-1⁄2 cups, about 15 minutes. Pour the thickened sauce over the ribs, sprinkle the diced mango on top, and serve.