Preheat oven to 400 degrees F (200 C). Brush two large baking sheets with the oil.
Cut the thinly-sliced sirloin into strips across the grain about 1/4 inch (1/2 cm) wide. Pound at least 3 times on each side to flatten with a metal or wooden mallet.
Peel, crush, and finely minced the garlic. Place in a large bowl. Mix in the salt, and sugar. Add the slices of meat and toss to coat thoroughly.
Arrange the beef among the prepared baking sheets, being careful not to overcrowd. Cook in preheated oven for 15 minutes. Without opening the door, turn off the oven and allow to rest for another 15 minutes. Remove from the oven and allow to cool to room temperature. Refrigerate or freeze in an airtight container until ready to use.
To cook, coat a frying pan with oil over medium heat. Fry the dried pieces of beef until crisp. Transfer to a towel-lined plate before serving.