Preheat the oven to 375 degrees F and grease a standard 12-cup muffin tin with nonstick spray.
Add the flour, oats, baking powder, baking soda, and salt to a medium bowl. Stir together.
Add the milk, maple syrup, oil, eggs, vanilla extract, strawberries, and lemon zest, if using. Stir together gently to just combine.
Evenly divide the batter among the muffin tin using about ¼ cup per cup.
Bake 16-18 minutes or until a cake tester inserted into the center comes out clean.
Remove from oven, let cool for a minute or two in the pan, and transfer muffins to cool fully on a wire rack. (Use a paring knife around the edges if needed to help you remove them from the pan.) Serve slightly warm or at room temperature.
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Notes
Store fully cooled muffins for up to 3 days in an airtight container in the fridge or 3 months in a zip top freezer bag in the freezer.Egg-free: Instead of the egg, use 2 tablespoons ground flaxseed and 1/4 cup water.Gluten-free: Instead of the whole wheat flour, use this cup-for-cup gluten-free flour mix. And use certified gluten-free oats.Dairy-free: Use an unsweetened plain nondairy milk for cow's milk.Mini muffins: Reduce baking time to 12-14 minutes to make 24 mini muffins.Dice the berries into small pieces to ensure the batter around them holds together well as they bake.Use a cake tester inserted into the center of the muffin to test for doneness. It should come out cleanly.Remove the muffins from the pan after they come out of the oven so they can cool on a wire rack, rather than continue to bake in the hot pan.Stir together 1/4 cup powdered sugar and 1 tablespoon milk to make an optional icing. Drizzle it over the muffins with a spoon.