Warm the olive oil in a skillet over medium heat. Add the finely chopped onion and sauté for 2 to 3 minutes until it becomes translucent and fragrant.

Toss in the minced garlic and sauté for an additional 30 seconds.

Stir in the drained black beans, ground cumin, smoked paprika, optional chili powder, salt, and black pepper. Cook for 2 to 3 minutes.

Remove the skillet from heat and mix in the chopped cilantro and lime juice.

Lay out the bread slices. Spread a thin layer of softened butter on one side of each slice. Flip half of the slices so their buttered side faces down.

Scoop the black bean mixture evenly over the unbuttered slices. Top with shredded cheese and cover with the remaining buttered slices.

Preheat the skillet over medium heat. Place the assembled sandwiches in the pan. Cook for 3 to 4 minutes per side.

Slice the sandwiches and serve warm.