Step 1

Prepare the following, adding each to the same large bowl as you complete it: Thinly slice 3 medium celery stalks crosswise (about 1 1/4 cups). Peel and thinly slice 2 large carrots crosswise (about 1 1/2 cups). Dice 1 large yellow onion (about 2 cups). Quarter 1 of the medium lemons, thinly slice each lemon wedge, removing and discarding any seeds and the pithy ends of the lemon.

Step 2

Heat 2 tablespoons of the olive oil in a large Dutch oven or other heavy-bottomed pot over medium-high heat until shimmering. Meanwhile, pat 1 pound boneless, skinless chicken thighs dry with paper towels. Season all over with 1 teaspoon of the kosher salt and 1/4 teaspoon black pepper.

Step 3

Add the chicken to the pot in a single layer. Sear until browned, 4 to 6 minutes per side. Meanwhile, mince 2 garlic cloves. Thinly slice 3 medium scallions crosswise (about 1 cup). Pick the leaves from 4 fresh thyme sprigs (about 1 teaspoon).

Step 4

Transfer the chicken to a plate (it will not be cooked through). Add the remaining 1 tablespoon olive oil to the pot and heat until shimmering. Add the scallions and cook until tender, 30 seconds to 1 minute. Add the carrot mixture and remaining 1/2 teaspoon kosher salt. Cook, stirring occasionally, until starting to soften, about 5 minutes. Add the garlic and thyme and cook, stirring often, until fragrant, about 1 minute.

Step 5

Return the chicken and any accumulated juices on the plate to the pot. Add 2 (32-ounce) cartons low-sodium chicken broth and bring to a boil. Reduce the heat to maintain a simmer and cook until the vegetables are tender and the chicken is cooked through, 2 to 10 minutes more. Transfer the chicken to a plate or clean cutting board and shred with 2 forks into bite-sized pieces. Return the chicken to the pot.

Step 6

Add 1 cup dried orzo pasta and cook, stirring occasionally, until the orzo is tender, 9 to 10 minutes. Meanwhile, finely grate the zest from the remaining lemon (about 1 1/2 teaspoons) and juice the lemon (about 1/4 cup). Finely chop the fronds and tender stems of 4 fresh dill sprigs (about 1/4 cup).

Step 7

Add the lemon zest, 2 tablespoons of the lemon juice, and dill to the soup, and stir to combine. Taste and season with more lemon juice as needed. Serve garnished with more chopped dill and scallions if desired.