Chop pecans to desired texture and toast in a dry skillet over medium heat until crisp and fragrant.
Meanwhile, place cheese, margarine, and marshmallows in a glass dish in microwave oven (cover with a paper towel). Melt for 4 minutes on .25 power. Stir. It's ok if the marshmallows are still a little lumpy.
While pecans toast and cheese melts, combine cake and pudding mixes, add eggs, and slowly moisten with milk until a thick batter is achieved.
Spread cake batter in a 9x13 baking dish. Sprinkle with toasted pecans, then with brown sugar. It's ok to have some clumps with bare batter peeking through.
Finally, pour or spoon cheese mixture over top in rivulets.
Bake at 350 degrees for 20-25 minutes, until cheese is barely scorching and a toothpick inserted in the middle comes out clean. (Be sure to stick the toothpick in a spot of cake only.)