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.