In a large bowl, add both packs of muffin mix, brown sugar, egg, butter and oats. Mix well. Press into a 9x13 baking dish which has been lightly sprayed with a non-stick spray. **if adding nuts and/or coconut, mix into mixture before pressing into baking dish**
Place the semi-sweet chocolate chips and sweetened condensed milk into a sauce pan and melt on low heat constantly stirring. Take off the stove as soon as everything is melted. Evenly drizzle on top of the muffin mixture. Bake in 350 degree oven for 35 minutes. Can serve warm or at room temperature.
Note: these can be heated in the microwave for a few seconds, if you want to eat the leftovers warm.