Cook bacon in a medium frying pan over medium-high heat until crisp. Transfer to a paper towel to drain. Pour off grease, then add shrimp to pan and cook until pink, about 1 minute, stirring often. Set aside.
Heat 1 tsp. oil in a large frying pan over medium heat. Set a tortilla in pan and sprinkle half of it with half the bacon, shrimp, cheese, and onions. Fold tortilla over filling and press down gently. Cook, covered, until browned, turning once, about 3 minutes total. Transfer to a plate. Repeat to make second quesadilla.
Cut each quesadilla into 4 pieces. Serve with avocado, salsa, and sour cream.
Note: Nutritional analysis is per quesadilla.