1. In a food processor, combine onion, 2 Tbsp. of the mint, parsley, rosemary, 2 Tbsp. of the oil, cumin, 1/8 tsp. of the salt, and red pepper flakes. Pulse to blend. The texture will be paste-like, similar to a pesto. Rub this mixture over the lamb pieces. Cover and marinate, refrigerated, at least 3 hours and up to overnight.
2. Prepare tzatziki. Finely chop remaining 2 Tbsp. mint. Add to a medium bowl and mix with yogurt, cucumber, garlic, remaining 1 Tbsp. oil, pepper, and remaining 1/8 tsp. salt. Refrigerate until ready to serve.
3. About 15 minutes before you're ready to grill the lamb, remove from the fridge. Also remove tzatziki from fridge; stir if needed to reblend ingredients. Preheat grill for medium-high heat and soak wooden skewers, if using, in warm water. Skewer 4 pieces of meat onto each skewer; discard any leftover marinade.
4. Oil grate. Grill lamb to desired doneness, about 3 minutes per side for medium-rare. Let rest 5 minutes, then serve lamb on or off the skewers. Serve tzatziki in a bowl on the side.
Source: Hannaford fresh Magazine, July - August 2015