Generously grease a heavy medium size shallow disposable foil pan.
Cut the sweet potatoes into thick slices, then place in a large bowl.
In a small bowl combine the brown sugar with thyme and lemon pepper; sprinkle over the potato slices in the bowl and toss to coat.
Arrange the slices in layers into the pan.
Dot with butter (at this point you may refrigerate until ready to grill).
Pour the orange juice over the top.
Cover with foil.
Place on the grill, then cover with the grill lid.
Cook for about 15 minutes, then remove the foil and do a test for doneness, if needed cook for additional time until they are to your liking, you may need to add in more orange juice if potatoes begin to dry out.