Mix the pumpkin puree, milk, white sugar, eggs, pumpkin pie seasoning and vanilla together in a large bowl.
Pour the mixture into a 12-inch cast iron skillet or a 9x13-inch casserole dish.
Whisk the oats, flour, brown sugar, cinnamon and salt together in a medium bowl.
Cut the butter into the mix using a pastry cutter or a fork until it forms a crumbly mixture.
Crumble the topping around the top of the pumpkin mixture.
Bake at 400°F for 30-40 minutes or until the center of the crisp jiggles only slightly and the top turns a light, golden brown.
Let it rest for 15 minutes before serving.
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