Step 1

Preheat oven to 425 degrees F. Coat a large rimmed baking sheet with cooking spray.

Step 2

Cut squash in half lengthwise and remove seeds. Cut crosswise into 1-inch slices.

Step 3

Combine 1 tablespoon oil, 1 1/2 tablespoons mustard, garlic, rosemary, lemon zest, 1/2 tablespoon lemon juice, 1/2 teaspoon pepper, and 1/4 teaspoon salt in a large bowl. Add chicken and the squash and stir to coat. Arrange in a single layer on the prepared pan.

Step 4

Bake, without stirring or flipping, until the squash starts to brown and the chicken reaches an internal temperature of 165 degrees F, 20 to 22 minutes. Transfer the chicken to a clean cutting board and slice.

Step 5

Meanwhile, whisk the remaining 2 tablespoons oil, 1/2 tablespoon mustard, 1 1/2 tablespoons lemon juice, maple syrup, thyme, and the remaining 1/2 teaspoon pepper and 1/4 teaspoon salt in a medium bowl. Add greens and toss to coat.

Step 6

Divide the greens among 4 serving plates. Top with the chicken and squash, Parmesan, and pumpkin seeds.