In a dry saucepan over medium-low heat, gently toast cumin seeds until just golden-brown and fragrant. Pour seeds into a spice mill or grinder (I use a re-purposed old coffee grinder) and pulse 3-4 times until just coarsely ground.

Mix together onion, parsley, oil, cumin seeds, cinnamon, salt and pepper in a medium-sized bowl. Pour half of the mixture into another empty medium-sized bowl. Add ground lamb to one bowl and ground beef to the other. Mix contents of each bowl gently, being careful not to overmix (I gently fold the mixture together with my hands).

Form 2.5 inch ovals of ground beef and ground lamb and place on a baking sheet brushed with oil. Cover lightly with plastic wrap and refrigerate at least two hours and up to 12.

Heat grill for direct heat (for a gas grill, heat to 350-400 degrees). Put each meatball on a skewer, packing them fairly tightly to help them stick together. Brush grill grid/grates with oil.

Grill kebabs, turning as needed until cooked through and a thermometer inserted in middles (avoiding skewers) registers 140 degrees (for medium-rare), 6 to 8 minutes.

Serve with pitas and accompaniments.