Preheat oven to 375 degrees. Line a standard muffin tin with paper liners or grease the muffin tin with oil.
Peel bananas and add to a large bowl. Use a potato masher or whisk to mash the bananas until no large pieces remain. You should have a heaping cup of mashed banana.
Add the eggs, oil, maple syrup, vanilla, and yogurt to the bowl. Whisk until well combined. Whisk in cinnamon, baking powder, salt, and baking soda. Using a spatula or large spoon, stir in flax and flour. It's ok if a few lumps remain. Fold in 1 cup of chopped strawberries.
Scoop the batter into the muffin cups, filling to the top. Add remaining diced strawberries to the top of the muffins.
Bake until tops are lightly browned and a toothpick inserted into the center of a muffin comes out clean, about 20 minutes.
Store at room temperature for one day then in the fridge for 3 days or freeze, well wrapped, for up to 2 months.