Heat broiler. Stir together mayonnaise and curry; set aside. In extra-large skillet heat 2 tablespoons olive oil over medium-high. Add potatoes; sprinkle with salt and pepper. Cook 6 minutes, turn; cook 6 minutes more or until crisp.
Combine turkey, 2 tablespoons of curry-mayonnaise, feta, and 1/4 teaspoon salt. Shape four 1/2-inch-thick patties. Broil 4 inches from heat 11 to 13 minutes (165 degrees F); turn once. Spread remaining curry-mayonnaise on bread; layer patties, onion, spinach, and feta. Serve with potatoes. Serves 4.