Preheat the oven to 95°C.
Spray 4 of the tortillas with cooking spray (or brush with olive oil). Lay the oiled tortillas on a large cutting board oiled-side down. Brush with the mustard and sprinkle with about half of the cheese. Top each evenly with a thin layer of ham, onions and some pepper, and then finish with the remaining cheese.
Brush the apple butter evenly on the remaining tortillas. Place one apple-butter tortilla on top of a ham-and-cheese tortilla (filling sides in), and firmly press the tortillas together to make a quesadilla.
Heat a large nonstick skillet over medium heat. Lay a quesadilla oiled-side down in the pan and cook until golden brown and the cheese starts to melt, about 2 minutes. Spray the top of the quesadilla with cooking spray, turn and cook until the other side browns and the cheese is melted, 2 to 3 minutes more. Transfer to a baking sheet and keep warm in the oven. Repeat with the remaining quesadillas.
Cut the quesadillas into 4 wedges and arrange on plates. Toss the apples with lemon and juice and cinnamon to taste. Serve with the apple slices.