Set oven to 350F / 177C.
In a large bowl, mix together the dry ingredients with a fork. In a smaller bowl mix together the wet ingredients until smooth. Add the wet ingredients to the dry ingredients and mix together using a spatula. Fold in the diced apple.
In a separate bowl, mix together the topping ingredients – it should be very crumbly.
Spray a muffin mold with avocado oil or nonstick spray. Evenly divide the batter among the muffin molds – I use an ice cream scoop to keep it uniform.
Add the crumbs topping to each muffin. And as an OPTIONAL step (and pro-tip), lightly pinch sugar on top of each one muffin for a crispier sugar coating after baking.
Bake for 25 – 30 minutes, or until the topping is golden brown and toothpick comes out clean once inserted.
Allow them to cool in the molds for at least 10 minutes before attempting to remove after baking.