Preheat oven to 450°. Place 10-inch cast iron skillet in oven and heat for 25 minutes.
Meanwhile, blend eggs in a blender, on high speed, for 1 minute. Gradually add milk, 2 Tbsp. melted butter, pumpkin puree and blend for 30 seconds, or until smooth. Add flour, cornstarch, and next 3 ingredients, blending till just combined.
Remove skillet from oven, add remaining butter, quickly swirling to coat. Pour batter into skillet and bake at 450° 20 minutes, or until puffed and golden brown around the edges.
Toss arugula with olive oil and lemon juice. Top Pancake with bacon, Thyme Roasted Onion and Arugula. Serve immediately.