Dressing: Whisk vinegar, sugar, mustard and garlic together. Slowly whisk in the olive oil. Taste for seasoning; add salt and pepper to taste.
Salad: Toast pine nuts in skillet until lightly browned. Set aside. In the same skillet, saute onions in oil, add vinegar and sugar to carmelize. Meanwhile, prepare the mango and blueberries, and wash and drain the greens. Toss all ingredients (onions, mango, blueberries, bits of goat cheese, and greens). Add 1/2 of the dressing. Taste and add more dressing to taste. Whisk vinegar, sugar, mustard and garlic together. Slowly whisk in the olive oil. Taste for seasoning; add salt and pepper to taste.