Preheat oven to 400°. Line a large rimmed baking sheet with parchment paper.
In a medium bowl, stir together yogurt, cucumber, garlic, lemon juice, dill, ½ teaspoon salt, and ¼ teaspoon pepper. Cover and refrigerate for at least 1 hour or overnight.
In a large bowl, stir together beef, onion, bread crumbs, parsley, eggs, cumin, remaining 3 teaspoons salt, and remaining 2 teaspoons pepper until well combined. Using a 1-ounce spring-loaded scoop, scoop beef mixture, and shape into meatballs. Place on prepared pan.
Bake until a food thermometer inserted in thickest portion registers 165°, about 20 minutes. Serve with tzatziki. Garnish with dill, if desired.
Notes
Kitchen Tip: For easy party prep, make the tzatziki and shape your meatballs the night before.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/greek-meatballs-with-tzatziki-recipe/