Make the pice de gallo: Combine the tomatoes, onion, jalapeño, cilantro, lime juice, and salt in a small bowl. Set aside.
To make the bean filling, add the black beans with their liquid, cumin, garlic granules, Mexican oregano, onion powder, salt, and pepper to a blender or food processor.
Blend into a smooth puree.
Pour the bean puree into a skillet over medium heat. Cook, stirring frequently, until the puree thickens enough to hold its shape when you drag a spoon through it, about 5 minutes.
Place the halved rolls cut-side up on a baking sheet and spread with the butter.
Broil until the edges are golden and crisp, 1 to 2 minutes.
Spread the bean puree evenly over the toasted rolls.
Top each roll evenly with Oaxaca cheese.
Broil until the cheese is melted, about 2 to 3 minutes.
Top the molletes with the pico de gallo and serve.