Preheat oven to 400ºF.
Scatter the baguette slices on a large baking sheet and drizzle with EVOO, salt and pepper. Put into oven and toast for a few minutes.
In a large skillet over medium heat, cook bacon until crispy, about 4-5 minutes. With a slotted spoon, remove bacon and reserve fat.
Add the onions to the hot bacon fat and caramelize for 10 minutes. Add in the apple. Season with salt and pepper; cook for another few minutes. Remove from heat and put into a serving bowl. Top with cheese and serve with crostini alongside.