To a large saucepan of boiling water add the sweet potatoes, return the water to a boil, then reduce the heat to medium-low, cover & simmer until tender, about 10 minutes. Drain well.
In a large nonstick skillet, warm oil over medium-high heat until hot but not smoking, then add chicken & saute until opaque & cooked through, about 2 minutes.
Reduce heat to medium & add the sweet potatoes, nectarine, marmalade, mustard & jalapeno, cooking & tossing gently until heated through, about 2 minutes.
Add the bananas & cook until heated through, 1 to 2 minutes.
Serve the mixture sprinkled with sliced scallions.