Preheat grill to high. Grill the sausages until golden brown on all sides and cooked through, about 10 to 12 minutes. Remove, let rest for 5 minutes and slice into 1/4-inch thick slices. Lay 8 of the tortillas on a work surface. Divide the cheeses, sausage, onion peppers, garlic and parsley among them. Stack to make 4 and top with the remaining 4 tortillas. Brush the tops with the olive oil and grill for 2 to 3 minutes until golden brown. Brush with more oil, turn over and continue grilling until golden brown and the cheese melts. Remove the quesadilla, quarter and top with the relish.
Combine all ingredients in a medium bowl and season with salt and pepper to taste.