Preheat oven to 375 degrees F. Grease or line a muffin tin. I love to use a silicone muffin tin or silicone liners to prevent sticking.
Combine all ingredients in a large, high-powered blender in the order they are listed: almond milk, maple syrup, eggs, Greek yogurt, vanilla, bananas, spinach, old fashioned oats, baking powder and soda, and sea salt. Blend until smooth, about 1 to 2 minutes. The batter should look like a green smoothie. The blender will be very full, so you can gently blend the wet ingredients before adding the dry ones to make more space if needed.
Pour batter to just about the top of each muffin cup. Put the muffin tin in the oven and back for 20 to 22 minutes, or until the muffins are very slightly brown on the top and a toothpick that you put in the center comes out clean.
Transfer the muffins to a wire rack to cool. Enjoy!
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Notes
Storage: Keep in a sealed container in the refrigerator for up to 5 to 7 days.
Freezing: Let the muffins cool completely. Wrap each one individually in plastic wrap or parchment paper to prevent freezer burn. Store in a freezer-safe bag or container for up to 3 months. Thaw in the fridge overnight or microwave in 20-second increments straight from frozen (remove the wrapping first) until warmed through.
You can try to make these muffins as mini-muffins. Just check to see if they are done around 15 to 17 minutes, instead of at 20 minutes.