
First, toast the pepitas in a skillet over medium heat until fragrant and making little popping noises, about 4 to 5 minutes. Transfer them to a bowl to cool.
Peel the rough skin from the beets with a vegetable peeler, then slice off and discard the tip and rough end of the beet. If you have a mandoline, use it to slice the beets into thin matchsticks (watch your fingers!). If you don’t have a mandoline, place the larger flat side against the cutting board and slice the beet into super-thin pieces. Working in reasonable batches, stack a few slices on top of each other and cut them into long, thin matchsticks.
In a medium-sized serving bowl, combine the beets, arugula, crumbled feta and pepitas. Drizzle in just enough dressing to lightly coat the salad once tossed. Toss and serve. (If you intend to have leftovers, wait to dress individual servings when you’re ready to eat them—store the salad and dressing separately in the refrigerator, covered, for up to 4 days.)