To prepare pico de gallo, combine first 8 ingredients in a medium bowl.
To prepare quesadillas, cook pancetta in a large nonstick skillet over medium-high heat until crisp. Remove pancetta from pan with a slotted spoon; place in a medium bowl. Add mushrooms to drippings in pan; sauté 6 minutes or until tender. Add mushrooms to pancetta in bowl; toss well.
Wipe pan clean with paper towels. Sprinkle 2 tablespoons cheese over each of 4 tortillas; top each with 1/2 cup mushroom mixture, 2 tablespoons cheese, and 1 tortilla. Lightly coat top tortillas with cooking spray. Heat pan coated with cooking spray over medium-high heat. Place 1 quesadilla in pan; cook 2 minutes on each side or until tortillas are lightly browned. Set aside and keep warm. Repeat procedure with remaining quesadillas. Cut each quesadilla into 6 wedges. Serve with pico de gallo and sour cream.