Preheat the oven to 350ºF. Line a 9 by 5-inch loaf pan with parchment paper.
Put the bacon in a medium unheated skillet over medium-low heat; cook until crisp, flipping once or twice, about 10 minutes. Transfer to a cutting board to cool, then finely chop or crumble.
In a large bowl, whisk together the almond flour, arrowroot, collagen, baking soda, and salt. Put the bananas, peanut butter, maple syrup, eggs, and vanilla in a medium bowl and whisk well. Add the banana mixture to the flour mixture and stir until well combined. If using the chocolate and peanuts, set aside
one tablespoon of each for garnish, then fold the remaining chocolate and peanuts and the chopped bacon into the batter.
Spread the batter evenly in the lined loaf pan. Sprinkle the reserved chocolate and peanuts on top, if using. Bake until a toothpick inserted in the center comes out clean, 45 to 50 minutes. Cover loosely with foil while baking if the top is browning too quickly.
Put the pan on a rack to cool for 10 minutes, then turn the bread out onto the rack to cool completely. Store leftovers covered in the fridge for up to 4 days, or wrap tightly and freeze for up to 3 months.