Preheat your oven to 400°F and toast the focaccia for 5 to 8 minutes. Toasting it really is better.
While the bread toasts, stir the mayo and pesto together in a small bowl to make your pesto mayo.
Cook the bacon to desired crispness.
Lay the focaccia flat, turn a serrated knife sideways, and slice through the middle so you have a top and a bottom. Keep the crumbly top flat and set it aside.
Spread a generous layer of pesto mayo on the bottom piece, then pile on the turkey, bacon, tomato, arugula, and red onion.
Dollop a little more pesto mayo on top of the arugula and onion, so you don't have to flip the top piece and lose the crumbles.
Gently press the top piece back on and give it a little squish so it is nice and secure.
Cut it down the middle and across a few times, about six pieces total. Serve right away and enjoy!