On work surface lay out two tortillas. Layer chicken, cheese and arugula on each; season with salt and pepper. Cover with remaining tortillas. Heat a griddle or two skillets and brush with oil. Carefully place quesadillas on griddle and cook until blistered and golden. Turn them with a large spatula and cook until golden. Meanwhile, stir cumin, cayenne and salt, to taste, into sour cream. Remove quesadillas and cut each into 6 pieces. To serve, dollop with cumin cream and top with salsa.