Heat a skillet over medium heat and add the canola oil. Add the onions and balsamic vinegar and cook, stirring often, until they begin to soften.
Reduce heat to medium-low and continue to cook, stirring often, until deeply golden (around 20 mins.).
For the Sandwich:
Place two paper towels on a plate. Arrange the slices of bacon on the paper towel, separately. Place 2 more pieces of paper towel on top of the bacon. (You may need to cook half of the bacon at a time, in order to fit the plate.)
Microwave on high until the bacon is slightly crispy, about 3 to 5 minutes. It will crisp up more as it cools.
Toast the bread slices and place the crispy bacon in between with the caramelized onions. Add some brown sauce or BBQ sauce and serve.