Preheat oven to 375°F. Line a 12-cup muffin pan or grease lightly.
Mash bananas in a large bowl. Whisk in milk, beaten egg, oil, vanilla, and sugar until smooth.
Stir in baking mix and cinnamon just until combined. Do not overmix.
Fold in nuts if using. Divide batter evenly among muffin cups. Sprinkle with coarse sugar if desired.
Bake 16–18 minutes, until golden and a toothpick comes out clean.
Cool in pan 5 minutes, then move muffins to a rack to finish cooling.
Notes
Variation: Stir in 1/2 cup chocolate chips or swap the nuts for sweetened coconut. For bakery-style tops, mound the batter slightly higher in the center and sprinkle with coarse sugar. Storage: Keep in an airtight container at room temperature for 2 days or freeze up to 2 months.This recipe is an original creation inspired by classic Easy Bisquick Banana Muffins flavors. All ingredient ratios and instructions are independently developed.