Heat butter in a heavy casserole or ovenproof skillet and brown the ham lightly. Add pineapple chunks, onion soup and 1 tablespoon of the brown sugar. Season with salt and pepper, to taste. Bring to a boil, then remove from heat. Place sweet potato slices in an even layer over the ham and pineapple mixture, with slices overlapping to make a cover. Combine pecans and the remaining brown sugar. Spread this over the sweet potatoes.
Bake for 30 minutes in a preheated 400°F. oven.