Puree all the ingredients except the pork belly and onions. Marinate the pork belly in this mixture for at least 2 hours. Cook the onions and marinated pork belly on a hot plancha or griddle until slightly charred, about 8 minutes. Chop the pork into bite-sized pieces.
Stir oil and garlic in a pot on low heat until the garlic browns. Roast the jalapeños and onion in a dry pan until almost black. Cool the garlic, oil, onions and jalapeños, then puree with the cilantro, salt, juices, and sesame seeds. Reserve.
Pour 2 tablespoons of oil on a griddle and place a tortilla flat on top of it and add 1 cup of cheese on half of the tortilla. Add the spicy pork on top of the cheese and fold over, cooking until the cheese has melted. Cut the quesadillas into four triangles and top with 2 tablespoons of salsa verde and 1 teaspoon of sesame seeds. Garnish with 3 sprigs of cilantro.