Soak the brown rice in hot, boiling water for 30 minutes before cooking. Drain and set aside. This softens the grains and helps them cook creamier in the milk.
Preheat the oven to 375°F. Grease an 8×8-inch baking dish.
Add the soaked rice and milk to a saucepan. Start on medium-high heat and stir occasionally so it doesn’t stick. Lower the heat as needed and simmer for 20-30 minutes, until the rice is tender and the milk becomes thick and creamy. Do not drain any milk. Keep it all for a pudding texture.
In a large bowl, whisk together pumpkin purée, molasses, maple syrup, vanilla, ginger, cinnamon, nutmeg, and salt.
Fold the milk-cooked rice into the gingerbread mixture. Stir in the pecans. Transfer to the prepared baking dish, cover with foil, and bake for 30 minutes. Remove the foil and bake another 15–20 minutes, until the top is golden and lightly crisp.
Remove from the oven, top with more crushed pecans, and serve warm.
For the optional maple glaze, whisk powdered sugar, maple syrup, and milk until smooth. Drizzle over the warm casserole before serving.