In a bowl, whisk the eggs with the sour cream, salt and black pepper. Melt the butter in a small skillet over medium heat. Pour in the egg mixture chopper green onions, jalapeño, and cook, stirring often, until the eggs are just set, about 2 minutes.
In a separate, large skillet, warm the tortilla over medium heat, flipping occasionally. Once the pan and tortilla are warm, sprinkle one-half of the cheese over one-half of the tortilla. Top the cheese with scrambled eggs, guacamole and press the empty tortilla halve over the toppings. Let the quesadilla cook until golden and crispy.
Remove the skillet from the heat and transfer the quesadilla to a cutting board. Let it cool for a few minutes to give it time to set, then slice each quesadilla into 2-3 slices with a very sharp knife. Serve immediately, with your favorite sauce.