Tuna Melt Quesadilla

Name: Tuna Melt Quesadilla
Cuisine: American, Mexican, Latin American
Ingredients: 1/2 140g can water-packed tuna, drained; 2 tablespoons mayonnaise; 1/2 red onion, finely diced; 1 garlic clove, minced; 1 small bunch fresh parsley, roughly chopped; 1 tablespoon capers, drained; 1 tablespoon olive oil, plus more for cooking; Kosher salt; Ground black pepper; 1 10-inch flour tortilla; handful of grated cheddar cheese