Heat oven to 425° F.
On a large rimmed baking sheet, toss the squash, tomatoes, and garlic with 2 tablespoons of the oil, ½ teaspoon salt, and ¼ teaspoon pepper.
Roast the vegetables until the squash is tender, 20 to 25 minutes.
Meanwhile, heat the remaining tablespoon of oil in a large skillet over medium heat.
Season the chicken with the coriander, ½ teaspoon salt, and ¼ teaspoon pepper. Cook until golden brown and cooked through, 6 to 7 minutes per side.
Serve the chicken with the squash and tomatoes and sprinkle with the oregano.