The masala (Indian spice mixture) will keep for up to four weeks refrigerated in an airtight container.
1. Heat 2 to 3 tablespoons oil in a wide nonstick pan on high heat. Add onions and reduce heat to medium. Lightly fry the onions for 3 to 4 minutes until onions are translucent and the edges are lightly browning. Reduce heat to medium-low.
2. Add curry leaves, ginger, garlic, and serranos and sweat for 1 to 2 minutes. Add remaining ingredients (sugar, soy sauce, vinegar, black pepper, salt) and mix thoroughly. Remove from heat. Cool completely, then blend to a smooth paste in a food processor or blender.
3. Season the lamb strips liberally with kosher salt and a light dusting of Indian chile powder. Let lamb sit for 10 minutes so salt incorporates into the meat and then liberally apply the marinade, using about a ¼ of a cup. Reserve leftover marinade for another use. Let meat marinade for at least 30 minutes and up to 6 hours.
4. Skewer the meat, leaving space between each piece to allow even heat distribution. Fire up your grill until very hot, then cook for 2 minutes per side for medium rare, and 3 to 4 minutes per side for higher levels of doneness.
5. Heat tortillas or naan directly on the grill. Serve lamb immediately with warm flour tortillas or naan with julienned red onions, lime, cilantro, and a small dash of yogurt.