Pasta salad meets egg salad meets finger food! Cook up a few extra shells in case some tear while draining or filling. You can cook the pasta and prepare the filling one day ahead (minus the arugula), and store in the fridge. Up to two hours before serving, stir in arugula and stuff shells.
1. Cook shells in large pot of boiling, salted water 12 minutes, or until tender, stirring to prevent sticking. Remove with slotted spoon, drain, then cool on sheet of foil. Cook beet in same boiling water 20 minutes, or until tender. Drain, cool, and peel beet, then finely dice.
2. Whisk together mayonnaise, 1 Tbs. vinegar, and mustard powder in bowl. Fold in eggs and beet. Whisk remaining 1 Tbs. vinegar with oil in separate bowl. Add arugula, and toss until arugula begins to wilt. Fold arugula into egg salad.
3. Spoon egg salad into shells. Sprinkle with microgreens (if using).