Preheat the oven to 400 degrees F. Line a rimmed sheet pan with foil or parchment. Rub the chicken breasts with 1 tablespoon olive oil and season with 3/4 teaspoon salt, 1/2 teaspoon pepper, and 1/2 teaspoon garlic powder on both sides.

Place the chicken on one half of the sheet pan. Toss the vegetables with 1 tablespoon olive oil and 1/2 teaspoon salt, then spread them on the other half of the pan in a single layer. Roast everything together for 22 to 26 minutes, until the chicken reads 165 degrees F on an instant-read thermometer and the vegetable edges are charred. Let the chicken rest on a cutting board for at least 5 minutes before you touch it.

While the oven does its work, cook the farro. Add the rinsed farro, chicken broth, and 1/4 teaspoon salt to a medium saucepan. Bring to a boil over medium-high heat, then reduce to a low simmer, cover, and cook for 20 to 25 minutes. Taste at the 20-minute mark. It should be chewy but not chalky at the center. Drain any remaining liquid, then let it sit uncovered for a few minutes to dry out slightly.

Make the dressing. In a small bowl or jar, whisk tahini and lemon juice together until combined. Add the grated garlic, salt, and pepper. Whisk in warm water one tablespoon at a time until the dressing pours in a slow ribbon. It should coat a spoon but not be stiff.

Slice the rested chicken breast thin, against the grain. Divide the farro evenly among four containers. Arrange a quarter of the sliced chicken and a quarter of the roasted vegetables over each portion.

Drizzle each bowl with about 2 tablespoons of lemon-tahini dressing, or store the dressing separately in a small jar and add it at lunchtime. Seal and refrigerate for up to four days.