This meatless lunch's ingredients are made from yesterday's dinner leftovers. (See White-Bean-Stuffed Portobellos.)
Toss sliced mushrooms with spinach and feta. Add lemon juice and olive oil. Season with salt and pepper and toss to combine. Rub toasted bread with garlic. Divide mashed beans among toasts. Squeeze lemon juice over toasts and drizzle with olive oil. Serve toasts alongside salad.