Prep Work: Scrub potatoes and cut to under 1" pieces. Cut arugula to bite sized pieces, wash, and dry. Combine dressing of olive oil through lemon juice in closed container.
Cover potatoes with water and bring to boil in pan, then reduce and simmer approx. 10 min. If using endive, add to pot for the last 5 min. Drain.
In serving bowl whisk together olive oil, onions, vinegar, mustard, zest and juice of lemon. Add 1/2 tsp. salt and 1/4 tsp. pepper (for yield of 6).
Add warm potatoes to dressing and toss gently. Fold in arugula.
(adapted from Cooking Light 2010 "Lemon-Arugula Potato Salad")