Preheat the oven to 325 degrees F (165 degrees C). Grease a 9x13 inch baking pan.
In a medium bowl, cream together the margarine and 1/2 cup brown sugar. Stir in the flour; the mixture should be crumbly. Sprinkle over the bottom of the prepared pan and pack down to cover.
Bake for 15 to 20 minutes in the preheated oven, until lightly toasted. Remove from the oven and immediately sprinkle with chocolate chips. When the chips have softened enough, spread them over the crust.
In a heat-proof bowl over simmering water, or in the microwave, combine the marshmallows, peanut butter, brown sugar and light cream. Cook, stirring occasionally until melted and smooth. Remove from heat and stir in the chow mein noodles. Spread on top of the chocolate layer of the crust. Let cool before cutting into squares.