Best-Ever Keto Quesadillas

Preheat oven to 400º and line two medium baking sheets with parchment paper. In a medium skillet over medium-high heat, heat oil. Add pepper and onion and season with chili powder, salt, and pepper. Cook until soft, 5 minutes. Transfer to a plate.  In a medium bowl, stir together cheeses. Add 1 1/2 cups of cheese mixture into the center of both prepared baking sheets. Spread into an even layer and shape into a circle, the size of a flour tortilla. Bake cheeses until melty and slightly golden around the edge, 8 to 10 minutes. Add onion-pepper mixture, shredded chicken, and avocado slices to one half of each. Let cool slightly, then use the parchment paper and a small spatula to gently lift and fold one side of the cheese "tortilla" over the side with the fillings. Return to oven to heat, 3 to 4 minutes more. Repeat to make 2 more quesadillas. Cut each quesadilla into quarters. Garnish with green onion and sour cream before serving.