Greek Turkey Burgers with Tzatziki Sauce

ground turkey

fresh spinach leaves, chopped

sun-dried tomatoes, chopped

red onion, minced

feta cheese, crumbled

garlic cloves, pressed or minced

egg, whisked

olive oil

dried oregano

kosher salt

soft whole-wheat hamburger buns

Bibb lettuce leaves

Sliced red oinon

cucumber, halved with skin and seeds removed

low-fat plain Greek yogurt

garlic cloves, pressed or minced

red wine vinegar

fresh dill, minced

kosher salt and freshly ground black pepper

freshly ground black pepper