In a large skillet, heat oil over medium-high heat. Saute red pepper and onion until soft, about 5 minutes. Add corn, red pepper flakes, cumin, and salt and pepper to taste. Toss to incorporate and saute for 3 minutes. Transfer to a bowl and add the cilantro. Preheat a long, 2-burner cast iron griddle, or a large saute pan over medium heat. Lay 2 tortillas on a work surface and spread each evenly with refried black beans. Place tortillas, bean side up, on the griddle (begin with 1 if using a saute pan). Sprinkle onion-red pepper mixture evenly over the top of each, then sprinkle evenly with the cheese. Cover with another tortilla coated with refried black beans and cook until cheese melts, about 4 minutes. Flip quesadillas to toast the other side. Slice each quesadilla into 8 wedges, sprinkle with cilantro, and serve with Lime-Cilantro Sour Cream.
In a small bowl, mix all ingredients together until combined. Season, to taste, with salt if needed.