1) Place the breadcrumbs in a large bowl. Cover with milk and soak for 2 minutes. Add the onion, the beaten egg, minced beef, lime juice, tomato ketchup, garlic powder, salt and paprika, and work the ingredients together with your hands or a wooden spoon just until combined. Form the mixture into 12 small 2 1/2-cm thick patties and refrigerate them for at least 45 minutes or up to 8 hours.
2) Heat the olive oil in a large heavy saucepan over medium-high heat. Add about half of the burgers and brown them on each side, flipping with spatula, 5-7 minutes. Set the fritas on the rolls and cook the remaining burgers.
Serve with generous amounts of tomato ketchup.