Combine tuna, black beans, and sour cream in a large bowl. Stir in corn, Buffalo wing sauce, garlic salt, and cumin.
Melt 1 1/2 teaspoons butter in a large skillet over medium heat. Add 1 tortilla and heat for 1 minute; flip. Spread 1/2 tuna mixture over tortilla, sprinkle with 1/2 Mexican cheese, and top with another tortilla. Cover the skillet; cook for 1 minute. Flip quesadilla, cover, and cook until cheese is melted, 1 to 2 minutes. Repeat with remaining butter, tortillas, and filling. Slice each quesadilla into 8 wedges.
