Heat oil in large nonstick skillet over medium-high heat. Add bell pepper, ginger and garlic and sauté 1 minute. Add all mushrooms and sauté until brown and tender, adding 2 to 3 tablespoons water if mixture is dry, about 10 minutes. Add spinach and green onions and stir until spinach wilts, about 2 minutes. Stir in soy sauce. Season to taste with salt and pepper. Transfer to bowl. Serve, passing lemon wedges to squeeze over.