In a large skillet, cook bacon over medium heat until crisp. Drain bacon on paper towels, reserving drippings in the skillet. Crumble bacon; set aside.
Add onion to reserved drippings. Cook for 15 to 20 minutes or until onion is very tender and golden brown, stirring occasionally.
Arrange onion on browned side of a flatbread. Sprinkle with blue cheese and bacon before returning flatbread to the grill. Sprinkle with thyme before serving. Cut into wedges. Makes 6 appetizer servings.