In a small bowl, add the finely chopped red onion or shallot and vinegar. Marinade for 8-12 minutes to mellow the flavor of the onion.
To the marinade mixture add the mustard, salt, marmalade, orange juice, and orange zest. Whisk to combine all ingredients, slowly add the oil. When the mixture has formed an emulsion, taste it and add additional salt and pepper to taste.
Divide the arugula between your salad plates, add your fruit choices and nuts. Lightly drizzle the dressing over the salad, sprinkle with course salt and cracked pepper and serve immediately.