Soak the Cashews: Place cashews in a bowl and cover with just-boiled water. Let soak for 5 minutes.
Prepare the Vegetables: Peel and thinly slice the red onion. Thinly slice the spring onions at an angle. Drain and rinse the black beans. Quarter the cherry tomatoes. Finely chop the coriander and red chilli (de-seed for less heat). Thinly slice the avocado.
Cook the Black Bean Salsa: In a hot non-stick pan, add 1 tablespoon or a few sprays of oil and fry the onions, spring onion, and chilli for 2 minutes, stirring continuously. Add cumin seeds, ground cumin, smoked paprika, tamari, citrus juice, and salt. Cook for 30 seconds, then add beans and tomatoes. Cook for 2 more minutes, mashing lightly.
Make the Cashew Cheese Sauce: Drain and rinse the soaked cashews. Blend with oat milk, garlic powder, lemon juice, and salt in a blender until smooth.
Assemble the Quesadillas: Heat a dry pan and warm a tortilla for 30 seconds. Spread about 3 tbsp of cashew cheese on the tortilla, add a portion of the bean mixture on one side of the tortilla, and top with avocado slices, chopped coriander, and chilli. Fold the tortilla over, cook until browned, then remove and slice. Repeat with remaining tortillas and ingredients.
Serve: Enjoy the quesadillas hot, with any remaining cashew cheese stored in the fridge for up to 5 days for other uses