1.) Make the cheese sauce: Add the cashews, nutritional yeast, lime, stone ground mustard and water to a blender. Blend until the sauce is creamy. Set it aside.
2.) Make the onion-pepper filling: Place a sauté pan over medium heat. Add the sliced onion and bell pepper. Stir in the cumin and chili powder. Cover and cook for 5 minutes, stirring occasionally so the veggies don’t stick to the bottom of the pan. Then stir in a tablespoon of water and continue cooking uncovered. When the water evaporates stir in another tablespoon of water, continuing to sauté until the onions are caramelized.
3.) Turn the heat to low. Pour the cheese sauce into the onion and peppers. Stir well and then cover with a lid so the mixture doesn’t dry out.
4.) Make the first quesadilla: Place a non-stick pan over medium heat. Let it heat for 5 minutes. Then place one of the tortillas into the pan. Set a timer, letting the first side toast for 2 minutes and then flip. Set the timer for another 2 minutes. As you wait, carefully scoop about ¼ of the filling onto the tortilla and spread it evenly, forming a single layer of peppers and onions. Layer ½ cup of spinach across the onions and peppers. Place the second tortilla on top of the spinach.
5.) Once the timer goes off or the bottom side is toasted, use a large spatula to carefully flip the entire quesadilla. Toast the second tortilla for 2-3 minutes.
6.) When the quesadilla is done transfer it to a plate. Repeat this process with the remaining filling to make a total of 4 quesadillas. Note that subsequent quesadillas may require less cooking time because the pan will be hotter. You may want to turn the heat down slightly after the first couple. Slice the quesadillas into triangular slices and serve!