Step 1Toast the mustard seed in a small skillet over low heat, about 1 minute. Remove from heat.
Step 2Mix together the yogurt, lemon, ketchup and sumac, then add the warm seeds. Chill before serving.
Step 1In a food processor, add the onion, jalapeno and cilantro and pulse a couple of times.
Step 2Place the ground beef in a bowl and add the onion mixture. Add the curry powder, cumin, ginger, coriander, cinnamon, pepper, nutmeg and salt. Mix completely. Divide into 12 patties. Cover with plastic wrap and chill.
Step 3Grill the burgers to desired doneness, about 2 minutes per side for medium.
Step 4Place each burger on a slightly toasted round of pita bread cut out with a 2 1/4 -inch cookie cutter. Top with a spoonful of chutney and a mint leaf. Top with a second piece of bread and pass the dipping sauce.