Blueberries should be firmly frozen when used in baking.
Preheat oven to 400 degrees. Grease an 8-inch round baking pan; set aside.
In medium bowl, combine flour, oats, sugar, baking powder and salt. In second bowl, combine milk, oil and egg. Pour at once into flour mixture. Stir just until moistened (batter will be lumpy). Fold in firmly frozen blueberries. Spoon batter into prepared pan.
Bake until cake is golden and pulls away from sides of pan, about 20-25 minutes. Cool on a rack for 5-10 minutes. Serve warm.
This cake would be good with a coffee cake topping: (1 Cup Brown Sugar, 1/4 Cup Flour, 1/4 Cup Melted Butter, 4 Teaspoons Cinnamon, and 1 Cup Chopped Nuts.) Or a sugared cream cheese topping (see Strawberry Cream Cheese Muffins.)