Autumn Mushroom on Toast

Ingredients

• 4 large portobello mushrooms, stems removed
• 1/4 cup olive oil
• 2 cloves garlic, minced or grated
• 1 teaspoon dried oregano
• Salt and freshly ground black pepper to taste
• 4 slices ciabatta bread
• 2 tablespoons butter, melted
• 2 cups baby spinach leaves