If using ground beef or ground pork, follow same instruction as ground turkey in steps 3 and 4, roasting in hot oven until burgers reach a minimum internal temperature of 160 degrees, 10-12 minutes.
If using bacon, cook while onion caramelizes in Step 5. Line a plate with a paper towel. Place a medium non-stick pan over medium heat and add bacon to hot pan. Flip occasionally until crisp, 6-8 minutes. Transfer to towel-lined plate to remove excess oil. Top burgers with bacon.