Cut each sprout in half and take out the tough outer leaves.
Dice bacon into small bits.
Cut onion into pieces that are roughly the same size as the sprouts
Take a quart ziplock bag (if you are lazy like me, or a bowl if you love washing greasy dishes) and put all the ingredients together. We put them in a bag and made my younger son mix them together. Since he's probably not going to touch them when they were cooked, I thought I'd put him to work on them to pay a price for his fussiness.
Line a baking sheet with foil and spread the mixture in an even, single layer.
Bake at 350 for 30-35 minutes, turning half-way through.
You might want to finish up by broiling them to get them properly carmelized. What I did was pre-cooked them, and then when it was time to re-heat, I broiled them to get them hot and crispy.
*You can cut and mix the vegetables and bacon ahead of time and put the ziplock bag in the fridge. This way, you can prep the veggies on the weekend and just pour them onto a sheet and cook them fresh if you prefer.