Place potatoes in a Dutch oven; cover with cold water to 2 inches above potatoes. Bring to a boil; reduce heat, and simmer 15 minutes or until very tender. Drain; place in a large bowl.
Heat oil and butter in a medium skillet over medium heat until butter melts. Split vanilla bean lengthwise; scrape out seeds. Add seeds and vanilla bean pod to oil mixture; cook 30 seconds. Remove pan from heat; let stand 10 minutes. Remove pod; discard.
Preheat oven to 375°.
Add 2 tablespoons sugar, 1 teaspoon salt, cinnamon, and milk to potatoes. Beat with a mixer at medium speed until smooth. Spoon potato mixture into an 11 x 7-inch baking dish coated with cooking spray.
Add oats, pecans, flour, remaining 1/4 cup sugar, and remaining 1/4 teaspoon salt to butter mixture; toss. Sprinkle over potato mixture. Bake at 375° for 35 minutes or until bubbly around the edges.
I made the recipe as written, including the vanilla bean, and it was so, so good! It was sweet without being cloyingly sweet. The vanilla streusel was so fragrant and delicious. I loved the oatmeal; it was a much better choice than marshmallows.