Fold bottom of dough over filling. Fold sides over. Roll up wrapper to enclose filling completely. Repeat with remaining filling and wrappers. Add half of blintzes, seam side down, and fry until heated through and golden brown and crisp on all 4 sides, about 10 minutes.
Drain blintzes briefly on paper towels.
Repeat with remaining blintzes. Arrange blintzes on plates. Place dollop of yogurt and spoonful of remaining onions alongside. Can be stored in an airtight container in refrigerator for several days. Serve with crackers or raw vegetables.