Cook the bacon until crisp and drain on paper towels. Slice sun-dried tomatoes and shred the cheese if not pre-shredded. Make sure all your ingredients are ready before starting.
Spread butter on the outer sides of the bread. On the inner side, layer pesto, bacon, sun-dried tomatoes, and shredded cheddar. Top with the second slice of bread, butter side out.
Heat your skillet over medium heat. Place the sandwich and cook for 3-4 minutes per side, pressing lightly with a spatula, until golden brown and the cheese is melted. Serve immediately.