Step 1

Working in 3 batches, heat 2 tablespoons canola oil in a large skillet over high. Add oyster mushrooms and shiitake mushrooms to skillet in a single layer; cook, stirring occasionally, until browned, 4 to 6 minutes. Transfer to a baking sheet. Sprinkle all mushrooms evenly with 1 teaspoon salt.

Step 2

Add sesame oil and remaining 1 tablespoon canola oil to skillet; heat over high. Add ginger, garlic, and white parts of scallions; cook, stirring often, until fragrant, about 1 minute. Add rice, soy sauce, vinegar, sugar, and remaining 1 teaspoon salt. Cook, stirring often, until rice is warm, about 2 minutes. Add greens in batches, stirring until just wilted before adding next batch, 1 to 2 minutes total. Stir in celery, celery leaves, green parts of scallions, and mushrooms. Cook, stirring often, until celery leaves are just wilted, about 2 minutes. Transfer to a serving platter; sprinkle with pepper.