In a large flat-bottomed nonstick sauté pan or Dutch oven, heat olive oil to medium high heat until hot and shimmering. Add onion slices and let soften, about 2-3 minutes. Drop in lemongrass paste, minced garlic, and ginger, tossing with onions 1-2 minutes until fragrant and soft. Season with salt and pepper. Add grated cabbage and chopped mushrooms, tossing to coat with onion mixture. Season with salt and pepper. Drizzle remaining 2 tablespoons coconut aminos and fish sauce over vegetables. Cook until soft, about 5-6 minutes, tossing every other minute or so. Toss in shredded chicken and mix. Taste and season with additional salt and pepper only if needed. Serve with additional coconut aminos and garnished with cilantro, and Sriracha.