A handy supermarket product--chipotle-flavor mayo--is the secret ingredient in this loaded sandwich. We love the convenience, but if you like, stir 1 teaspoon of minced chipotle peppers in adobo sauce into regular mayonnaise instead.
In a small bowl, combine shredded cheddar cheese, mayonnaise and diced pimiento. Spread mixture evenly on bread slices. Divide spinach, chicken and tomato slices among four of the bread slices. Top with remaining four bread slices, spread side down.
Toast sandwiches in a panini press or indoor covered grill until bread is golden brown.