8 ounces lean ground pork
8 ounces lean ground turkey
1/3 cup old-fashioned oats
4 tablespoons ketchup
1 tablespoon spicy brown mustard
1 teaspoon soy sauce or Worcestershire sauce
12 teaspoon finely chopped fresh oregano, plus more for garnish, optional
2 large egg whites
1 medium red onion, grated (about 1/3 cup)
Kosher salt and freshly ground black pepper