Heat 1 tbs oil in a large frying pan over medium-high heat. Add walnuts and cook, tossing constantly, for 3 minutes or until hot. Remove and set aside.
Add remaining oil to the frying pan and heat until hot. Add garlic and mushrooms, reduce heat to medium and cook for 4-5 minutes or until mushrooms are tender. Stir in lemon juice and cook for 30 seconds.
Place spinach leaves, walnuts and feta into a large bowl. Spoon over the mushroom mixture and season with salt and pepper. Toss gently to combine.
Serve with crisp sourdough bread.