In a medium bowl, whisk together flour, baking soda, and salt. Set aside.
In a large mixing bowl, beat butter and brown sugar until light and fluffy. Beat in egg and vanilla. Add flour mixture. Stir in oats.
Press into a greased 9x13 baking pan. Bake for 10-15 minutes or until golden brown. Cool on a wire rack.
In a microwave-safe bowl, melt caramels and water; stir until smooth. Spread over crust. Sprinkle with the chips, nuts and M&M’s. Gently press into the caramel mixture.
Melt white chocolate; drizzle over the top. Let stand for 5 minutes or until coating is set. Cut into bars.