Drain cashews and add them to a blender with water, milk of your choice, garlic, sun-dried tomatoes, basil, salt and pepper. Blend until smooth. Tip: If you want the sauce to be thinner, add a little extra water.
Heat a skillet to medium-high heat. Add olive oil and onions to the pan. Cook for 10-15 minutes, stirring occasionally until tender and golden brown.
Preheat oven to 375 degrees. Place chicken cubes in a bowl with olive oil, oregano, red pepper flakes, salt, pepper and panko breadcrumbs. Toss together and press the breadcrumbs into the chicken so that it sticks. Place crusted chicken on a parchment lined baking sheet. Bake for 7 minutes until cooked through.
To assemble the quesadillas, smear them with cashew sauce. Top with caramelized onions and chicken then fold in half. Place in a non-stick skillet on medium high heat. Cook 3-4 minutes per side until golden brown.
To serve open the quesadillas, add in arugula and extra sun-dried tomatoes. Close and enjoy!