Preheat oven to 350°F. Cook bacon in a large nonstick skillet over medium heat until crispy, about 8 minutes. Drain on a paper towel–lined plate, then chop.
In a large bowl, mix cream cheese, mayo, sour cream, garlic powder, most of the cooked bacon (save some for topping), most of the jalapeños (reserve some for topping), and 1 cup each of cheddar and Monterey Jack. Season with salt and pepper.
Transfer mixture to a small oven-safe skillet or baking dish. Sprinkle remaining 1/2 cup each of cheddar and Monterey Jack, cooked bacon, and jalapeño on top.
Bake until dip is golden and bubbly, 15 to 20 minutes. (Optional: Broil for 3 minutes for extra golden cheese.) Serve with tortilla chips or baguette slices.