Combine the shallot, both mustards, lemon juice, olive oil, salt, and pepper in a jar with a tight-fitting lid. Shake vigorously for about 30 seconds until the dressing is emulsified and well combined. Set aside—this can be made up to a day ahead. I always use freshly squeezed lemon juice here because it gives the dressing much brighter acidity than bottled, which really makes the salad sing.

Bring a large pot of salted water to a boil and add the potatoes, cooking for about 15 minutes until fork-tender. While the potatoes cook, bring a separate pot of salted water to a boil for the green beans. Once the potatoes are done, remove them and cut into 1-inch chunks. In the same water, blanch the trimmed green beans for 30-60 seconds until bright green but still crisp, then immediately transfer to an ice bath to stop the cooking and preserve their vibrant color. Drain well before using.

While the potatoes and green beans are cooking, bring another pot of salted water to a boil and cook the pasta until just al dente (firm to the bite)—don't overcook or the salad will become mushy. Drain and set aside. While the pasta cooks, prepare all your vegetables: shred or cut the chicken into bite-sized pieces, dice the cucumber, cut the tomatoes into wedges or chunks, slice the pepper into thin strips, and roughly chop the onion. Hard-boil the eggs if not already done, then quarter them. Having everything prepped before assembly makes the final steps quick and stress-free.

Drizzle 3 tablespoons of the vinaigrette over the warm cooked potatoes and toss gently to combine—this allows the potatoes to absorb flavor while still warm. In a large bowl, combine the potatoes with the cooked pasta from Step 3, blanched green beans from Step 2, chicken, tomatoes, cucumber, pepper, onion, olives, and capers. Pour the remaining vinaigrette over everything and toss thoroughly until all components are evenly coated and combined.

Transfer the salad to a serving bowl or plate and arrange the quartered hard-boiled eggs on top as an elegant garnish. The salad can be served immediately while still slightly warm, or chilled for a couple of hours if you prefer it cold. Either way, give it a gentle toss just before serving to redistribute the dressing.