It's unclear when the term "qingxin" (literally "light and fresh") became fashionable. In fact, many vegetables belong to this category. They don't require elaborate cooking; simply blanching or steaming them, then seasoning them, makes for a delicious dish.
Vegetables with a firm texture, such as kale, choy sum, mustard greens, broccoli, celery, lettuce stem, and bitter melon, do not become overly soft after blanching, and their color becomes even more vibrant. For softer leafy greens like bok choy, Malabar spinach, crown daisy, lettuce, and spinach, a quick dip in boiling water is all it takes to enjoy their natural flavor.
To avoid the dish being too bland, you can try a few seasoning methods. The first is similar to "white blanching," which involves simply drizzling a sauce of light soy sauce and fermented black bean sauce over the vegetables. The second is "dipping sauce," such as one made from light soy sauce, sesame oil, and vinegar, which is savory, aromatic, fresh, and slightly sour. You can also add minced garlic or chili to enhance the flavor. The third is a simplified version of the "pa" technique (a method from Shandong cuisine), such as "scallion pa" or "cream pa," which involves adding broth to the blanched vegetables and thickening it with a light starch slurry. The fourth and simplest method is to toss the blanched vegetables with a salad dressing.