In a large pot, heat 1 tablespoon neutral cooking oil over medium heat until hot. Add the sliced onion and cook, stirring occasionally, for 5 minutes until softened and beginning to brown.
Add the garlic and ginger and cook for 1 minute until fragrant.
Add the sliced mushrooms to the pot and add the 1 teaspoon sesame oil. Cook, stirring occasionally, for 6-8 minutes or until the mushrooms begin to soften and darken around the edges.
Pour the vegetable stock into the pot and scrape up anything stuck to the bottom. Bring to a boil.
Stir in the Shaoxing cooking wine, soy sauce, and sambal oolek. Reduce heat to medium and cook over a low boil for about 20 minutes. Taste and season to your preferences.
Right before serving, stir in the baby spinach and half the minced scallions. Simmer over low heat until ready to serve.