Lightly mist a small nonstick skillet with olive oil spray (or substitute with butter or bacon fat) and place it over medium heat. Add the onion and pepper. Cook, stirring occasionally, for 6 to 9 minutes, or until they are crisp-tender and lightly browned on the outside.

Meanwhile, place a nonstick frying pan, large enough for a tortilla to lie flat, over medium-low heat. Put the tortilla in the pan. Sprinkle on the cheese evenly, covering the tortilla. Let the cheese melt.

When the onions and peppers are cooked, transfer to a bowl and cover to keep warm. Mist the skillet again with spray and add the eggs. As they begin to set, use a wooden spoon to scrape from one side of the pan to the other, to "scramble" them. Continue scrambling until no runny egg remains. Then spoon the eggs over the cheese on one half of the tortilla. Sprinkle the onion-pepper mixture over that. When the cheese is melted, fold the bare half over the filled half.

Transfer the quesadilla to a serving plate and cut into 4 wedges. Top with the salsa. Serve immediately.