Preheat the oven to 375 degrees. Line a bread pan with foil or parchment paper, leaving enough that you can grab it from above the pan side walls after baking.
Mix the ⅓ cup rolled oats, ⅓ cup milk, ¾ teaspoon salt, and ¼ teaspoon pepper. Let this soak while you move onto the next step.
Heat 1 tablespoon olive oil on a skillet over medium heat. Add the ⅓ yellow onion and 1.5 tablespoon minced garlic and saute until golden brown.
Add all the meatloaf ingredients (1 pound ground bison, 1 egg, 1 tablespoon Worcestershire sauce, the sauteed veggies, and the oat milk mixture) to a large bowl and mix with your hands gently until just combined. DO NOT OVER MIX or it will be tough and gummy.
Add the meatloaf mixture to the foil-lined bread pan, making sure it's spread evenly throughout the pan. Bake for 25 minutes.
While the meatloaf bakes, mix the ½ cup ketchup, ½ tablespoon pure maple syrup, 1 tablespoon yellow mustard, and ½ tablespoon chipotle peppers in adobo in a small bowl.
Remove the meatloaf from the oven and spread the glaze on the top evenly. Return to the oven and broil on high for 5 minutes.
Remove from the oven and leave it to rest for 10 minutes before removing and slicing.