1Position rack in center of oven and preheat to 350°F. Line 2 large rimmed baking sheets with parchment paper. Whisk flour, baking soda, cinnamon, and salt in medium bowl to blend. Using electric mixer, beat butter and both sugars in large bowl until smooth. Beat in egg and vanilla. Add flour mixture and oats and stir until blended. Stir in all chocolate chips and cranberries.
2Drop batter by rounded tablespoonfuls onto prepared sheets, 2 inches apart. Bake cookies, 1 sheet at a time, until edges are light brown, about 16 minutes. Cool on sheets 5 minutes. Transfer to rack; cool completely.
3Stir chopped milk chocolate in top of double boiler until melted and smooth. Using small spoon, drizzle melted chocolate over cookies in zigzag pattern. Let stand until milk chocolate sets, about 1 hour. (Can be made 2 days ahead. Store in airtight container at room temperature.)