In a medium size bowl, combine the flour, baking powder and salt. In another bowl, combine the oil, lemon, sugar, egg, milk and lemon zest. Mix well.
Add this mixture to the dry ingredients and mix just until combined. Do not overmix!
Divide the batter among 12 muffin cups that have been lined with a cupcake liner.
In a small bowl, mix together the ingredients for the topping until you have coarse crumbs.
Sprinkle 1 tablespoon streusel topping on the top of each muffin.
Bake the muffins for 5 minutes at 425 degrees, then, without opening the oven, lower the oven temperature to 375 degrees and bake for an additional 8 minutes. A toothpick inserted in the center of a muffin should come out clean.