1 1/2 tablespoons Sherry vinegar or red wine vinegar
Freshly ground black pepper
1/2 cup plain sheep's-milk or cow's whole-milk yogurt
1/4 cup chopped fresh mint
Crushed red pepper flakes (for serving)
A spice mill or a mortar and a pestle
Directions
Toast chiles, red pepper flakes, and cumin seeds in a dry small skillet over medium heat, tossing occasionally, until fragrant and cumin seeds are golden, about 3 minutes.
Let cool. Working in batches, finely grind in spice mill, then transfer to a blender. Add vinegar, paprika, and garlic to blender and blend until smooth. With motor running, gradually stream in oil and blend until combined. Transfer to a large bowl; season with salt.
Do ahead: Chile sauce can be made 2 days ahead. Cover and chill.
Pulse onion, chopped garlic, parsley, oregano, sage, fennel seeds, coriander, cumin, and 1 tablespoon salt in a food processor, scraping down sides as needed, until finely chopped. Add egg, lamb, and flour and pulse until evenly combined. Form lamb mixture into 1 1/2" balls.
Heat 2 tablespoons oil in a large skillet, preferably cast iron, over medium-high. Working in 2 batches and adding another 1 tablespoon oil to skillet if needed, cook meatballs, turning occasionally, until browned on all sides and cooked through, 5–8 minutes. Transfer meatballs to paper towels to drain.
Transfer all meatballs to bowl with chile sauce and toss to coat. Toss cucumber in a medium bowl with lemon zest, lemon juice, vinegar, and remaining 2 tablespoons oil; season with salt and pepper.
Spoon yogurt into bowls. Evenly divide meatballs among bowls; top with dressed cucumber and mint and sprinkle with red pepper flakes.
Do ahead: Meatball mixture can be made 1 day ahead. Cover and chill.
