Trim the lamb into 3/4-inch pieces and set aside.
Place the onions and jalapeño into a blender and blend until completely smooth, do no clean the blender. Pass through a fine mesh strainer set over a large bowl and press on the solids to extract as much juice as possible. Discard the solids.
Add all remaining ingredients except the lamb to the now empty blender and blend until smooth. Add this to the onion juice and then toss the lamb with the marinade. Marinade overnight and up to 2 days, turning half way through to ensure even application of the marinade.
When ready to cook, thread the meat onto skewers, preferably metal ones (if using wooden skewers, be sure to soak them in water for 30 minutes first or else they will burn during cooking). Be sure to leave a bit of space between each piece of meat on the skewer, you should have 4-8 skewers.
Grill or broil to your desired doneness. These are best cooked over a charcoal grill on coals that are evenly glowing orange for about 8-10 minutes total, flipping half way through. Test a piece of meat to determine if it is cooked - it should be cooked through but still tender.
Serve with chutney, sliced onions (soak in water for 15 minutes to remove any bite, if preferred), sliced tomatoes, fresh herbs, citrus wedges, and chutney.