Preheat and prep. Heat your oven to 375°F (190°C). Line a 12-cup muffin tin with liners or lightly grease it.
Mix the dry ingredients. In a large bowl, whisk together the flour, oats, baking powder, baking soda, cinnamon, nutmeg, and salt.
This helps keep the muffins light and evenly seasoned.
Combine the wet ingredients. In a separate bowl, stir together the mashed banana or applesauce, plant milk, maple syrup (or coconut sugar), oil, vanilla, and vinegar. The vinegar reacts with baking soda for better lift.
Bring it together. Pour the wet mixture into the dry ingredients. Stir gently with a spatula until just combined. Do not overmix or the muffins can turn dense.
Fold in mix-ins. Add blueberries, grated carrot, nuts, or chocolate chips—whatever you like.
Fold until evenly distributed. If using frozen berries, add them straight from the freezer and don’t over-stir.
Fill the tin. Divide the batter evenly among the 12 cups. They should be about 3/4 full.
Sprinkle toppings if using.
Bake. Bake for 18–22 minutes, or until the tops are set and a toothpick comes out with a few moist crumbs. If using very wet mix-ins (like zucchini), you may need an extra 2–3 minutes.
Cool. Let the muffins rest in the pan for 5 minutes, then move them to a wire rack. Cool completely for the best texture and to keep liners from sticking.