Preheat the oven to 350. Grease a 9x13 casserole dish with oil and set aside.
Bring a large pot of water to a boil, add the carrots, and cook until tender about 15 minutes; drain. Combine the carrots with the remaining ingredients in a food processor and process until smooth, scraping down the sides of the bowl as necessary. Depending on the size of your processor, you may need to do this in batches.
Spoon the mixture into the prepared casserole dish.
Combine the brown sugar, pecans, flour and butter in a medium bowl. Stir to blend. Scatter the mixture over the top of the casserole and bake until the topping is lightly browned, 55 minutes to an hour.