Cook and stir onions in skillet on medium heat 3 to 5 min. or until crisp-tender; transfer to medium bowl. Cool.
Add next 5 ingredients; press half into 10x6-inch rectangle on bottom of 13x9-inch baking dish. Top with spinach, eggs and carrots; cover with remaining meat mixture. Pinch edges together to seal. Top with bacon.
Bake 55 min. or until done (160F).
Let stand 10 min. before removing meatloaf from dish and slicing to serve.