Preheat the oven to 350°F. Grease a 2-quart casserole dish lightly with coconut oil or nonstick spray and set aside.
In a medium pot, add the carrots and sweet potatoes and cover with water. Bring to a boil and cook just until the chunks are tender, about 15 minutes. Drain well and cool for 5 minutes.
In a large bowl, mash together the carrots and sweet potatoes with the remaining base ingredients. Taste and adjust seasonings. Spread in the casserole dish and smooth the top.
While the vegetables cook, make the topping. In a mini food processor or Magic Bullet, blend all topping ingredients, except for the oats, until a crumble is formed. Stir in the oats by hand. Sprinkle the mixture evenly over the casserole base.
Bake for 35-40 minutes, rotating the dish once about halfway through baking, until the topping is browned. May be frozen.
Variation: If you prefer a more classic casserole, substitute another medium sweet potato for the carrots.