In a large frying pan over medium heat, heat 1 tablespoon of the oil until it shimmers. Add the onion, garlic and remaining 1/4 teaspoon of salt and cook, stirring frequently, until the vegetables start to soften, about 3 minutes. If using squash, add it along with the remaining 1/4 cup (60 milliliters) of water, reduce the heat to medium, cover and cook, stirring occasionally, until the squash is very soft, 20 minutes. Uncover, increase the heat to medium-high, and cook, stirring, until the extra water has evaporated, 2 to 3 minutes. If using mushrooms, cook uncovered over medium-high heat, using tongs to toss frequently, until they wilt, then reduce the heat to medium and cook, stirring and scraping the bottom of the skillet occasionally, until they are soft and starting to brown, 20 minutes. Taste, and season with more salt as needed. Turn off the heat and let cool.
Source: https://www.washingtonpost.com/food/2021/12/19/butternut-squash-mushroom-quiche-recipe/