Cut dinner rolls vertically into ½” slices. Lay slices on a baking sheet and brush both sides with olive oil.
Bake roll slices for 1-2 minutes on each side at 350 degrees or until golden brown. Set aside.
Meanwhile, cook bacon in a pan or skillet until crispy. Remove cooked bacon from pan, leaving some of the bacon fat. Chop bacon into small pieces.
Chop onion into slices. Cook in the pan with bacon fat over medium-low heat until caramelized.
Top the toasted crostinis with the cooked bacon pieces and caramelized onion. Bake until warmed through.