Cook the pasta by adding the penne to a large pot of salted boiling water.
Stir occasionally and cook until al dente, about 10-12 minutes or according to package directions.
Drain the pasta and rinse under cold water to cool it down slightly and stop the cooking process.
While the pasta is cooking, prepare the vinaigrette.
In a small bowl or jar, combine the fresh orange juice, balsamic vinegar, olive oil, brown sugar, and Dijon mustard.
Add a pinch of salt and pepper.
Whisk or shake vigorously until the dressing is well combined and emulsified.
Set aside.
In a large serving bowl, combine the shredded fennel, radicchio strips, chopped oranges, and optional red onions.
Add the cooled pasta to the bowl with the vegetables.
Pour the prepared vinaigrette over everything and toss gently to combine, ensuring all are lightly coated.
Garnish with toasted walnuts and fresh parsley just before serving. This salad can be served immediately or chilled for later.
