Preheat oven to 375F. Toss 2 400-g pkgs squash pieces with 2 tsp vegetable oil. Spread in 1 layer on a large rimmed baking sheet. Add 2 peeled large green bananas and 4 unpeeled garlic cloves. Roast until squash is very tender, about 30 min. Let cool slightly and peel garlic cloves. Mash garlic and bananas with 1/4 cup warm vegetable broth and 1 tbsp butter until smooth. Add squash and mash until chunky.