Heat the olive oil, orange juice and brown sugar together in a medium saucepan over moderately high heat. Stir until sugar is dissolved. Add the strawberries and plum pieces and cook until they begin to release their juices, about 2 minutes. Transfer fruit to a glass bowl with a slotted spoon.

Add the balsamic vinegar, salt, and pepper to the pot. Cook the sauce 3 to 4 minutes until thickened. Pour sauce over the berries. Let stand to cool, at least 5 minutes.

Toss fruit and sauce with greens and pine nuts. Divide salad among four salad plates and place one tablespoon of goat cheese, if desired on each plate and serve immediately.