Place the bacon in a large skillet and cook over medium-high heat, turning occasionally, until almost browned, 2 to 3 minutes. Add green onion to bacon; cook and stir until onion is soft and bacon is crisp, 3 to 5 minutes more.
Spread mayonnaise on one side of each slice of toast. Spread mashed avocado onto one side of one piece of toast. Top avocado with tomato slices, sprouts, and bacon mixture; sprinkle with salt and black pepper. Place remaining slice of toast on top.