Heat vegetable oil in a large saucepan over medium heat.

Add minced onion to the saucepan and cook until softened, about 2-4 minutes, stirring occasionally.

If desired, add minced garlic to the saucepan and stir.

Add the drained and rinsed black beans to the saucepan.

Add the drained corn kernels (or fresh corn) to the saucepan.

Stir in the salsa and red pepper flakes.

Cook the mixture until heated through, about 3-4 minutes, stirring occasionally.

In a large skillet over medium heat, melt 1 teaspoon of butter (or heat 1 teaspoon of vegetable oil).

Place one flour tortilla in the skillet.

Sprinkle cheese evenly over the tortilla in the skillet.

Spread some of the black bean and corn mixture evenly over the cheese.

Top with another flour tortilla.

Cook the quesadilla until golden brown on the bottom, then flip and cook until golden brown on the other side and the cheese is melted.

Melt more butter (or heat more oil) as needed, and repeat with the remaining tortillas and filling until all ingredients are used.

Serve warm.