Heat oil in a large skillet over medium heat. Brown steak strips on all sides. With a slotted spoon, transfer steak strips to a baking dish. Stir garlic into skillet; cook 5 minutes. Add vinegar, sugar, and ketchup. Then stir in mustard, paprika, salt, and pepper; and simmer 3 minutes. Pour sauce over steak strips.
Cover baking dish, and bake in a preheated oven for 1 hour. Uncover, and bake for 30 minutes more.