In a blender or food processor, puree the onions. Strain through a fine-mesh sieve into a 2-cup measuring pitcher, pressing firmly with a rubber spatula or the back of a wooden spoon to extract all the juice. Discard the solids. To the onion juice, add the lemon juice and enough water to measure 1 1/2 cups liquid. In a large bowl, combine the onion juice mixture and the bulgur and soak for 10 minutes. Add the beef, pine nuts, garlic, salt, cumin, cinnamon, cardamom and pepper to the bulgur and stir to mix well.
Using a little less than 1/3 cup for each kebab, form the beef mixture into 16 sausage links, each about 4 inches long and 3/4 inch in diameter. Thread onto the skewers. If the mixture is too crumbly, add water 1 tablespoon at a time, just until it holds together. Cover the prepared skewers and refrigerate until ready to cook.
Prepare a hot fire in a charcoal grill or heat a gas grill or broiler (grill). Away from the heat source, lightly coat the grill rack or broiler pan with cooking spray. Position the cooking rack 4 to 6 inches from the heat source.
In a small bowl, whisk together the yogurt, tahini, lemon zest and mustard. Cover and refrigerate.
Place the kebabs on the grill rack or broiler pan. Grill or broil the kebabs, turning as needed, until evenly browned, about 8 minutes. Drizzle with the yogurt sauce and garnish with the cilantro.