In a large mixing bowl, cream the butter and sugars. Beat in eggs and vanilla. Combine the flour, baking soda, salt and cinnamon; gradually add to creamed mixture. Stir in the oats, rhubarb, chips and cranberries.
Drop by tablespoonfuls 2 inches apart onto parchment paper lined baking sheets. Bake at 350 for 10-12 minutes or until set. Remove to wire racks to cool.
In a microwave-safe bowl, melt white chocolate; stir until smooth. Drizzle over cookies; let stand until set. Store in an airtight container.