01 - In a large mixing bowl, combine diced turkey, chopped spinach, shredded cheddar cheese, and red onion until evenly blended.
02 - Warm a large non-stick skillet over medium heat and lightly brush with olive oil.
03 - Spread one fourth of the filling mixture evenly on half of a tortilla, then fold the tortilla over to enclose the filling.
04 - Place folded tortilla in the skillet and cook for 2-3 minutes per side, or until golden brown and the cheese has melted.
05 - Repeat with remaining tortillas and filling, adding more olive oil to the skillet as needed.
06 - Slice each quesadilla into wedges and serve warm.