Preheat oven to 450 degrees F. Put a baking sheet into the oven to preheat.
In a large bowl combine 1 tablespoon of the canola oil with 1 teaspoon of salt and 1/4 teaspoon pepper. Add the sliced potatoes to the bowl and toss to coat. Remove the baking sheet from the oven, and add the potato slices, making sure they are all in a single layer. Transfer to the oven and bake for 8 minutes.
In a skillet, heat the remaining 2 tablespoons of the oil over medium heat. Add the onion and saute for 2 minutes. Stir in the garlic and spinach and saute for another 2 minutes.
In a large bowl whisk together the eggs, milk and remaining salt and pepper. Mix in the cheese and the onion and spinach mixture and set aside.
Spray an oven-proof skillet with nonstick cooking spray. Turn the oven down to 350 degrees F. Remove the potatoes from the oven and add them to the skillet. Pour in the egg mixture and transfer the skillet to the oven. Bake until the eggs have set, about 30 to 35 minutes.
Remove from oven and let cool for 5 minutes. Serve warm or at room temperature, directly from the skillet.