1Spread pesto and mayonnaise on one slice of bread. Layer meats, cheese, and peppers to make a sandwich. Top with second slice of bread.
2Spread top bread slice with half of butter.
3Heat a grill pan over medium heat and spray with cooking spray. When pan is hot, place sandwich butter-side down. Top with a brick covered in foil or another pan and press down. Cook for 2 to 3 minutes until golden brown. Butter top bread slice with remaining butter before turning over panini.
4Grill and press for another minute or two until panini is toasted and cheese is melted.