I made these brownies using Egg Beaters (although I have an egg allergy I'm able to tolerate these better than whole eggs, but you'll need to make other substitutions if these don't work for you) and substituting oil for butter.
1 pkg Betty Crocker Gluten Free Brownie Mix
1/2 cup Egg Beaters
3 Tbsp cooking oil
1/2 cup almonds (or whatever nut you prefer)
1 cup mini marshmallows
Combine Brownie Mix, Egg Beaters, and oil. Bake as directed on the box, minus 5 minutes. Remove from the oven 5 minutes early and sprinkle with marshmallows & nuts. Return to oven for final 5 minutes or until marshmallows start to melt. Remove and allow to cool.