Preheat oven to 400°F. Brush squash flesh with oil, season lightly, and roast cut-side down 35–40 minutes until tender.
Meanwhile whisk soy sauce, brown sugar, rice vinegar, sesame oil, garlic, and ginger in a bowl; set aside.
Heat 1 tbsp oil in a skillet over medium-high. Season chicken with salt and pepper and cook until browned, about 6–8 minutes. Remove.
Add remaining oil, pineapple, and sauce to pan. Bring to a simmer, stir in cornstarch slurry to thicken. Return chicken and toss to coat.
Shred squash with a fork, divide into bowls, top with teriyaki chicken, sesame seeds, and green onions.