Lightly coat the inside of a 4- to 6-quart slow cooker with cooking spray or a thin smear of butter or coconut oil to help prevent sticking.
In a small saucepan over low heat, warm the almond milk with the pumpkin pie spice, cinnamon and orange zest just until it begins to steam (do not boil). This helps bloom the spices and deepens the flavor.
Transfer the warmed spiced almond milk to a mixing bowl. Whisk in the pumpkin puree, maple syrup and vanilla until smooth. Stir in the water and salt.
Place the steel-cut oats in the prepared slow cooker and pour the pumpkin-liquid mixture evenly over the oats. Give everything a quick stir to combine and make sure the oats are submerged.
Cover and cook on LOW for 6 to 8 hours. If you have a programmable slow cooker, set it for about 7 hours then switch to the warm setting. About halfway through (around 3–4 hours in), open and give the oats a gentle stir to prevent them settling into a dry layer on the bottom.
When the oats are tender and creamy, turn off the slow cooker and let the porridge sit, covered, for 10 minutes to thicken slightly. Stir once more before serving.
While the oats rest, toast the chopped pecans in a dry skillet over medium heat, stirring frequently, until fragrant and lightly browned (about 3–4 minutes).
Spoon the oatmeal into bowls and top each serving with toasted pecans. Add a drizzle of maple syrup and a splash of almond milk if you like a looser texture.
To store: cool the oatmeal to room temperature, transfer to an airtight container and refrigerate for up to 5–7 days. Reheat gently on the stovetop or in the microwave with a little extra almond milk to loosen.