"Oat streusel" refers to a crumbly mixture made of oats, sugar, butter, and sometimes other ingredients, that is used as a topping to add texture and flavor to baked goods such as muffins, pies, or cakes. Full definition
I could literally go on and on about my new favorite muffins - Strawberry Banana Muffins with Oat Streusel Topping. (kimscravings.com)
These vegan blackberry muffins are made with a lightly sweet whole wheat batter with a hint of cinnamon and sprinkled with a light brown sugar oat streusel topping. (connoisseurusveg.com)
These Healthy Cinnamon Pumpkin Muffins are made with whole wheat flour and applesauce and have a lightly sweet oat streusel topping. (whitelightsonwednesday.com)