Preheat your oven to 400°F and line a large baking sheet with parchment paper. While the oven heats, finely chop the spinach into roughly 1/4-inch pieces, mince the garlic, finely dice the red onion, and chop the fresh mint. Crumble the feta cheese into 1/2-inch chunks and zest the lemon. Having everything prepped before you start mixing ensures the meat mixture stays cool and won't become tough from overworking.

In a large bowl, whisk together the room-temperature eggs until just combined. Add the chopped spinach, mint, diced red onion, minced garlic, breadcrumbs, salt, pepper, and lemon zest to the eggs. Gently fold these ingredients together until just mixed. Add the ground turkey and feta cheese, then fold everything together with your hands using a light touch—work quickly and avoid overmixing, as this keeps the meatballs tender. I find that mixing with your hands for about 30-45 seconds is ideal; overworking develops gluten in the breadcrumbs and makes the meatballs dense.

Using a 1.5-ounce cookie scoop or your hands, form the mixture into balls roughly the size of golf balls (about 2 inches in diameter). Place them on the prepared baking sheet, spacing them about an inch apart to allow air circulation and even cooking. Bake for 18-20 minutes until the internal temperature reaches 165°F when measured with a meat thermometer in the center of the largest meatball. For the best texture, I like to check the temperature of at least two meatballs to ensure they're cooked through—turkey can dry out if overcooked, so pulling them at exactly 165°F keeps them juicy.

Remove the meatballs from the oven and let them rest on the baking sheet for 5 minutes before serving. This brief rest allows the residual heat to finish cooking the center while the exterior sets, ensuring they stay moist. Transfer to a serving platter and serve warm with tzatziki on the side for dipping.