Preheat the oven to 400ºF and line muffin tins with liners or spray with cooking spray.
In a small nonstick skillet, lightly toast the mixed nuts until fragrant and beginning to brown. Set aside.
Wash and coarsely chop the cranberries and set aside.
In a large bowl, mix the flour, baking powder, soda and salt well. Next, add the oats and mix well.
In another bowl, cream the egg and sugars until frothy.
Add the yogurt and vegetable oil to the creamed sugar and mix well.
Add the wet ingredients to the dry and mix until blended, but do not over mix.
Add the coarsely chopped cranberries and gently fold in.
Scoop the muffin batter into the muffin pans and set aside while you prepare the topping.
In a small bowl, mix together the 5 tablespoons of granulated sugar, 2 tablespoons of flour and the cinnamon. Next, add 1/4 cup of finely chopped mixed toasted nuts. Using a pastry cutter or fork, cut in the cold butter until the mixture becomes a crumbly topping.
Sprinkle the muffin batter with streusel topping and a little bit more chopped nuts. Bake for 15 minutes or until golden brown.
Serve warm by themselves, or with a little butter. They can be stored in an airtight container on the counter for about 2 days, or in the fridge for up to a week.
