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 six 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 five 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 two minutes. Add ketchup, red pepper flakes and cayenne pepper. Cook for another five minutes. Remove from heat and stir in scallions. Cool before serving.