Preheat the oven to 400°F (200°C). Line a baking sheet with parchment or lightly oil it.
In a large bowl, combine the ground turkey, breadcrumbs, Parmesan, parsley, oregano, minced garlic, egg, and a pinch of salt and pepper. Mix until just combined.
Shape the mixture into meatballs about 1 to 1 1/4 inches in diameter and arrange them on the baking sheet.
Bake for 20–25 minutes until golden and cooked through (internal temperature 165°F / 74°C).
While the meatballs bake, prepare the tzatziki: Grate cucumber, sprinkle with salt, let sit for 5 minutes, then squeeze out excess moisture.
Stir the drained cucumber into Greek yogurt with lemon juice, minced garlic, and salt. Adjust flavor to taste.
Serve meatballs warm with tzatziki.
Notes
If your turkey is very lean, adding olive oil or milk can improve texture. For dairy-free tzatziki, substitute yogurt and omit the Parmesan.