Can you use steel-cut oats instead?

I would think that you could replace the rolled oats with steel-cut oats, but you would have to adjust the recipe and the texture in the end wouldn't be the same. Steel-cut oats take a lot longer to cook than rolled oats and require more liquid, but you could try partially cooking the steel-cut oats on the stovetop according to their package instructions before mixing them with the other ingredients and baking it. It might take a bit of experimentation to get the new proportions just right, but it's worth a try.