Cooking spray 
4 (6-ounce) salmon fillets (about 1 inch thick) 
½ teaspoon salt, divided 
¼ teaspoon black pepper 
1 teaspoon olive oil 
1 tablespoon thinly sliced shallots 
1 ½ cups presliced mushrooms 
2 cups fresh spinach 
1 teaspoon grated lemon rind 
1 teaspoon fresh lemon juice

Heat a large nonstick skillet coated with cooking spray over medium-high heat. Sprinkle fish with 1/4 teaspoon salt and pepper. Add fish to pan; cook 5 minutes on each side or until fish flakes easily when tested with a fork. Remove fish from pan, and keep warm.

Add oil and shallots to pan; sauté 1 minute. Add mushrooms in a single layer; cook 2 minutes (do not stir). Cook an additional 2 minutes, stirring frequently. Add spinach; cook 30 seconds or until spinach wilts. Remove from heat; stir in 1/4 teaspoon salt, rind, and juice. Serve over fish.