Vegetarian Pesto, Tomato, Spinach and Cheddar Melt
Lightly spread both slices of bread with margarine or butter. On non-buttered side, spread one slice of bread with pesto and with mayonnaise. Place one slice of sharp cheddar cheese on top of pesto mixture, followed by slices of baby spinach leaves, tomato, caramelized onions, and remaining slice of bread butter-side up. Heat skillet on medium heat. Toast sandwich until golden. Flip sandwich and cook until remaining side is golden or cheese is melted.