Lamb Meatballs with Cucumbers and Herbs

Name: Lamb Meatballs with Cucumbers and Herbs
Ingredients: ½ small red onion, very thinly sliced; ⅓ cup golden raisins; ¼ cup red-wine vinegar; 1 teaspoon whole coriander seeds; 1 teaspoon cumin seeds; ½ teaspoon Aleppo pepper, plus more for serving; ½ teaspoon ground cinnamon; Kosher salt (we use Diamond Crystal) and freshly ground black pepper; 1 pound ground lamb; ½ bunch fresh parsley; 1 bunch fresh mint; 1 bunch fresh dill; ½ cup plain (or fresh) breadcrumbs; 1 egg, lightly beaten; 2 cloves garlic; 6 Persian cucumbers, halved and thinly sliced on the bias; Extra-virgin olive oil; ½ cup labneh, or sheep's-milk or Greek-style yogurt; 1 lemon