Chicken Parmesan-Stuffed Spaghetti Squash

Preheat oven to 400 degrees F. Cut squash in half lengthwise; scoop out and discard seeds. Place squash, cut-side down, on a parchment paper-lined rimmed baking sheet. Bake until tender when pierced with a knife, about 40 minutes. (Alternatively, place 2 squash halves in a large microwaveable dish with 2 tablespoons water; microwave on High until tender when pierced with a fork, about 11 minutes. Repeat with the remaining squash halves.) Let the squash cool for 10 minutes. Scrape out the strands with a fork, leaving a 1/2-inch border on the sides and bottom of each shell. Place the squash strands in a large bowl and set aside.

Increase oven temperature to 450 degrees F. Heat oil in a large skillet over high heat. Add chicken; cook, stirring occasionally, until just browned, about 2 minutes. Add onion and garlic; cook, stirring occasionally, until soft, about 4 minutes. Remove from heat; stir in marinara sauce and crushed red pepper. Add the chicken mixture to the bowl with the squash; toss to combine. Spoon the mixture evenly into the squash shells. Top with mozzarella and Parmesan.

Bake until the cheese is melted, 8 to 10 minutes. Let stand for 5 minutes before serving.