Preheat oven to 400°F (200°C).
Place jalapeño halves cut side down on a baking sheet and roast for about 15 minutes, or until skins begin to blister. Let cool, then peel off skins if desired.
Spread butter evenly over one side of each bread slice.
In a small bowl, mix the cream cheese, cheddar, and Monterey Jack cheeses.
Place two bread slices butter side down on a skillet over medium heat. Spread cheese mixture evenly on each slice.
Top with roasted jalapeños and cooked bacon.
Place remaining bread slices on top, butter side up.
Cook until golden brown on the bottom, about 3–4 minutes. Flip carefully and cook the other side until golden and the cheese is melted, about 3–4 more minutes.