Preheat the broiler. Arrange the tomatillos, onion wedges, garlic and chiles on a baking sheet. Spray with cooking spray and season with salt and pepper. Broil, turning often with tongs, until charred all over. Peel and stem the chiles and place in a food processor along with the chiles, tomatillos and onion. Add the cilantro, lime zest and juice, agave and cumin. Process the salsa until coarsely chopped. Transfer to a bowl; season to taste.
Heat a large skillet or griddle over medium to medium-high. Spray the pan and cook 1 or 2 tortillas, depending on the pan size, until lightly golden, 30 to 60 seconds; flip and place some cheese, chicken, red onion and pickled jalapeños on one half of the tortilla. Fold over and cook, flipping occasionally, until the tortilla is golden and the cheese melts, about 3 minutes. Repeat with remaining tortillas and ingredients. Cut quesadillas into wedges and top with the salsa and crema.