Add 1 ¼ cups rolled oats to a clean coffee grinder or mini food processor. Pulse until the oats are finely ground, to the texture of flour (you might have to do this in a couple of batches if using a coffee grinder).
Whisk together the ground oats, the remaining 1 ¼ cups rolled oats, ¾ cup brown sugar, 1 Tablespoon baking powder, 1 teaspoon baking soda, and ½ teaspoon table salt in a large bowl. Set aside.
In a small bowl or large measuring cup, whisk together ½ cup plain or vanilla Greek yogurt, ½ cup milk, ¼ cup canola oil, 2 large eggs, and 2 teaspoons vanilla extract.
Pour the wet ingredients into the dry ingredients and mix with a hand mixer on low speed until the dry ingredients are incorporated. Increase the mixer to high speed and mix for an additional two minutes. Cover the bowl with plastic wrap or a lid and place in the fridge to rest for at least an hour, or up to 12 hours, or overnight.
Heat the oven to 400°F. Prepare a 12-cup muffin pan by lining the cups with paper liners or greasing the cups with neutral-flavored cooking oil. Fold ½ cup chocolate chips into the batter with a spatula. Divide the batter evenly among the muffin cups. Top each muffin with a sprinkle of extra chocolate chips or turbinado sugar, if desired.
Bake the muffins for 20-25 minutes or until a toothpick comes out with just a few crumbs clinging to it. Cool the muffins for 10 minutes before serving. Store any leftovers in a zipper bag in the freezer and thaw at room temperature or for a few seconds in the microwave.
Notes
Instead of using ½ cup each Greek yogurt and milk, you could use 1 cup of regular yogurt, buttermilk (liquid or powdered), or soured milk (1 Tablespoon lemon juice or vinegar with enough milk to equal 1 cup). Use your favorite dairy-free yogurt and milk to make this recipe dairy-free.