Grease and flour a 12-cup muffin tin. Heat the oven to 375 F.
Combine the topping ingredients in a small bowl and set aside.
Combine the flour, baking powder, soda, and salt; whisk to blend well and set aside.
In a mixing bowl with electric mixer, beat the brown sugar and butter together until light and fluffy. Add the eggs and beat until well blended. Add the vanilla, pineapple, and 1 cup of the chopped pecans or walnuts.
Add the flour mixture to the pineapple mixture and stir just until ingredients are all moistened and blended. Do not overmix.
Fill the prepared muffin cups about 2/3 to 3/4 full and sprinkle with the topping mixture.
Bake pineapple muffins for about 20 to 25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.