Prep: *If you have time, drain, rinse, and dry chickpeas in advance – this allows them to crisp up more in the oven. Preheat the oven to 425F and prep all the vegetables. Set a baking sheet aside.
Roast: add the chickpeas, capers, a drizzle of olive oil, and salt to a large bowl and mix well. Spread across 2/3 of the baking sheet. Toss the potatoes in the same bowl with oil and salt, then transfer to the other 1/3 of the sheet. Roast on the top rack of the oven for 30 minutes.
Make the Dressing: in the meantime, whisk the lemon juice, oil, mustard, shallot, chives, thyme, and salt and pepper together in a small bowl until emulsified. Toss the green beans and radishes with salt and oil in the same large bowl as before, then set aside.
Get it Crispy: remove the baking tray from the oven and push the chickpeas to the side – they should be crispy. Add the green beans and radishes to the center of the tray, then roast on the top rack of the oven for an additional 13-15 minutes.
Serve: Transfer the roasted elements to a large tray, then add on the tomatoes, olives, and dressing. Niçoise salad is usually served with the elements divided and at a slightly warm or room temperature, but you do you!