Preheat oven: Preheat the oven to 425°F and line a large baking sheet with parchment paper for easy cleanup.
Season and roast squash: Toss the cubed butternut squash with 2 tablespoons olive oil, half the salt, and half the pepper. Spread in a single layer and roast for 25 minutes, until the edges turn golden brown and the cubes are fork-tender.
Season the chicken: While the squash roasts, pat the chicken thighs dry and season both sides with the remaining salt and pepper.
Sear the chicken: Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Sear the chicken thighs for 6-7 minutes per side, until golden and cooked through to 165°F internally.
Rest and slice chicken: Transfer the chicken to a plate and let it rest for 5 minutes, then slice into bite-size strips.
Sauté the garlic: In the same skillet, lower the heat to medium and sauté the minced garlic for about 30 seconds, until fragrant but not browned.
Build the sauce: Pour in the chicken broth and heavy cream, stirring to combine, then whisk in the parmesan cheese until the sauce thickens slightly, about 3-4 minutes.
Cook the tortellini: Add the fresh tortellini directly into the simmering sauce and cook for 4-5 minutes, stirring occasionally, until tender.
Combine everything: Fold the sliced chicken, roasted butternut squash, and chopped sage into the skillet, stirring gently to coat everything in sauce.
Simmer and serve: Simmer for 2 more minutes to let the flavors settle, then serve hot with extra parmesan on top.