Preheat oven to 350°F.
Pierce the sweet potatoes 6 times.
Place on a microwaveable plate and microwave for 6 minutes, rotating halfway through.
Once cool enough to handle, peel the sweet potatoes and cut them up into large chunks.
Spray a 13 X 9-inch baking dish with cooking spray and set aside.
Arrange sweet potatoes and half of the pecans in prepared baking dish. Set aside.
Combine corn starch and light brown sugar in a small saucepan.
Gradually add orange juice, whisking to blend.
Cook the orange juice mixture over high heat, stirring constantly, until mixture boils. Reduce heat and simmer for 3 minutes.
Remove from heat and stir in butter and vanilla.
Pour the mixture over the sweet potatoes.
Bake for 40 to 45 minutes, or until edges are browned and bubbly.
Remove from oven and top potatoes with mini marshmallows and remaining pecans.
Return to oven; bake for 3 to 4 more minutes, or until marshmallows begin to melt and nuts start to brown.
Remove from oven and serve.