Preheat the oven to 400°F.
Line a baking sheet with aluminum foil. Lay the bacon on the baking sheet in a single layer and transfer to the oven. Let the bacon cook for 20 to 25 minutes, until just crispy, turning the bacon over once in the middle of the cooking time. Remove the baking sheet from the oven and transfer the bacon to a paper towel–lined plate to cool. Once the bacon is cool enough to touch, chop it into bite-size pieces and set aside.
Cut each avocado in half lengthwise. Remove the pit from the avocado and discard. Remove the avocado from the skin, and place the avocado flesh in a bowl.
Add the cilantro, cotija cheese, serrano pepper, lime juice, salt, and pepper to the bowl. Mash with a fork until half smooth and half chunky. Fold in half of the bacon. Taste and add more salt and pepper if desired. Garnish the guacamole with the remaining bacon, and add more crumbled cotija cheese if desired.
Serve immediately with tortilla chips.