Sauté the onion, bell pepper, and mushrooms in a large saucepan over
medium heat until the onion turns translucent and starts to brown, about 8
minutes. Add water 1 to 2 tablespoons at a time to keep the vegetables from
sticking.
Season the vegetables with sea salt and black pepper to taste. Stir in the
cheese sauce and cook until heated through. Set aside.
Heat a large skillet over medium heat for a minute. Place a tortilla on your
work surface and spoon on one-third of the vegetable mixture, then place
another tortilla on top of it. Transfer the quesadilla to the skillet and heat
until lightly browned, about 2 minutes. Carefully turn the quesadilla over and
brown the other side. Repeat with the remaining tortillas and vegetables.
To serve, cut each quesadilla into 6 wedges and serve with the salsa andsour cream.