In a large bowl, beat butter and sugars until creamy.
Add eggs and vanilla; blend.
In a separate bowl, sift together the flour, baking soda, cinnamon, nutmeg and salt. Add this to the creamed mixture.
Stir in oats and rhubarb until combined.
Stir in chocolate chips and walnuts, if desired.
Drop cookies by large spoonfuls onto prepared pan. Bake for 8-12 minues.