Preheat the oven to 375°F. Line a rimmed baking sheet with parchment or lightly oil it.
In a medium bowl, whisk the egg, lemon juice and lemon zest. Stir in the chopped parsley, dill and minced garlic.
In a large bowl combine the ground turkey, finely chopped red onion, panko, crumbled feta, oregano, smoked paprika, salt and pepper. Pour the egg-herb mixture over the turkey and gently fold with a fork or spatula until everything is evenly distributed — avoid overworking so meatballs stay tender.
Use a tablespoon or small scoop to portion the mixture and roll into compact 1 to 1 1/4-inch balls (you should get about 18–20). Place them on the prepared sheet about 1/2 inch apart. Refrigerate the tray for 10 minutes to help the meatballs hold their shape while baking.
Brush the tops of the chilled meatballs with a little olive oil. Bake at 375°F for 20–22 minutes, turning the pan once halfway through so both sides brown evenly. They’re done when an instant-read thermometer reaches 165°F and the outsides are lightly golden.
While the meatballs bake, make the cucumber–tomato salad: toss the diced cucumber, tomato, red onion and parsley with 1 tablespoon olive oil, 2 tablespoons lemon juice and a pinch of salt and pepper. Taste and adjust acidity or seasoning; chill until ready to serve.
When the meatballs are out of the oven, let them rest 5 minutes on the baking sheet. This gives juices time to redistribute and makes them easier to handle.
Serve the meatballs over cooked grain with a spoonful of cucumber–tomato salad, a generous dollop of tzatziki, extra crumbled feta and Kalamata olives. Finish with an extra squeeze of lemon if you like.