In a small dry skillet over medium heat, toast the walnuts, tossing or stirring frequently, until fragrant, 3 to 5 minutes. Remove from the heat, transfer to a small bowl, and let cool.

Using a sharp paring knife, trim the top and bottom off the grapefruit. Stand it on one end and, cutting downward following the curve of the fruit, remove all the rind and white pith. Hold the fruit over a medium bowl and cut each grapefruit segment from its membrane, letting the segment drop into the bowl. Squeeze any juice from the remaining membrane into a small bowl or jar.

In another medium bowl, whisk together the oil, vinegar, honey, salt, pepper and 1 Tbsp of the grapefruit juice. (Reserve the remaining juice for another use, such as drinking it!) Just before serving, add the radicchio to the bowl with the dressing and toss to coat.

To serve, arrange about ¾ cup of the radicchio onto each plate then evenly divide the grapefruit segments, onion, goat cheese and the walnuts over each portion. Alternatively, you can also arrange the salad in a large salad bowl and serve it family-style.