Preheat the oven to 400℉. Line a large baking sheet with parchment paper.
Slice the bolillos in half lengthwise and spread ½ tablespoon of butter on each slice.
Heat a large skillet over medium-high heat. Place the bread in the skillet buttered side down, and toast for 3-5 minutes until lightly golden brown.
Place the toasted bolillo halves on the prepared baking sheet buttered side up and top each half with a layer of ¼ cup refried beans and ¼ - ½ cup shredded cheese.
Bake in the oven for 12-15 minutes until the cheese has melted and is bubbly. Make sure to keep an eye on it during this time as the bread can quickly start to burn.
Top each slice with 2 tablespoons of pico de gallo or fresh salsa and some diced avocado. Serve immediately.
Notes
Cheese: Instead of shredded Monterey Jack cheese, you can use any other melty cheese you have on hand. A classic Mexican melty cheese that's often used is Chihuahua cheese, or you could also use Mozzarella.
Bolillo Bread: If you can't find bolillo bread rolls, you can use telera bread or any French bread.
Refried Beans: Refried black beans are more traditionally served with molletes, but refried pinto beans also work!
Butter: Adding salted butter adds more depth of flavor, but you can omit it completely or use unsalted butter or margarine.
To make the molletes a bit more filling, you could also add crumbled chorizo, shredded chicken, or ground beef.