In a large bowl, using your hands mix together pork, coriander, curry powder, Worcestershire, cayenne, scallions and garlic, seasoning well with salt and pepper. Make 6 even patties and put in refrigerator until ready to cook. Heat a large fry pan over medium-high heat, add oil. Sear patties until golden brown on both sides and cooked through, about 5 minutes per side. Cook in batches, if necessary. Serve inside hamburger buns topped with lettuce leaf, tomato slice and spicy ketchup.
In a saucepan over medium heat, lightly saute garlic in butter, about 2 minutes. Add ketchup, red pepper flakes and cayenne pepper. Cook another 5 minutes. Remove from heat and stir in scallions. Cool before serving.