Preheat oven to 400°F (205°C). Line a sheet pan with foil for easy cleanup.
Toss chicken with 1 tbsp oil and ranch seasoning. Rub squash halves with remaining oil, cut-side down on the sheet pan.
Arrange chicken and veggies around squash. Roast 30–35 minutes until chicken reaches 165°F and squash strands easily with a fork.
Flip squash, scrape strands into a small mound on pan, sprinkle cheese over chicken and squash, and return to oven 3–5 minutes to melt.
Season to taste, garnish with parsley, and serve straight from the pan.