Prepare barbecue (medium-high heat). Brush grill rack with oil.
2
Gently mix turkey, onion, 1/3 cup feta, 3 tablespoons chopped olives, 1 1/2 teaspoons olive oil, garlic, rosemary, generous 1/2 teaspoon coarse salt, and generous 1/2 teaspoon pepper in medium bowl. Form into 4 patties, each about 1 inch thick. Spray with Pam and sprinkle with salt and pepper.
3
Grill burgers until charred on both sides and cooked through, about 5 minutes per side. Server on toasted buns if desired along with tzatziki sauce.