Apple Walnut Skillet Muffin

Normally I make muffins from scratch, but I had some muffin mix in the pantry that I wanted to use up, and I thought I'd do something different with it. Different flavors of muffin mix would work too, and you can use a pan that is a little smaller (it just might have to bake longer). As always, real maple syrup, no fake stuff!

2 7 oz packets Apple Cinnamon Muffin Mix
1/2 cup milk
1/2 cup maple syrup
2 cups granny smith apples, peeled and sliced
1 tsp lemon juice
1/2 cup maple syrup
1/2 tsp salt
1/2 cup chopped walnuts

Spray an 11" cast iron pan with baking spray. Preheat oven to 425. In a medium bowl, combine muffin mix, milk and 1/2 cup syrup. Mix until just combined, pour into prepared pan.
In a large bowl, combine remaining ingredients. Spread on top of batter.
Bake approx 25 minutes or until golden brown.
1 tsp cinnamon