In a skillet over medium heat, add olive oil and sliced onions. Cook, stirring occasionally, for about 15-20 minutes until the onions are caramelized. Remove from heat and let cool slightly.
In a bowl, mix mayonnaise with half of the caramelized onions and balsamic vinegar. Set aside.
In a large skillet, cook the ground beef over medium-high heat, breaking it apart with a spatula. Season with garlic powder, onion powder, salt, and pepper. Cook until browned and cooked through, about 7-10 minutes.
To assemble the bowls, divide the salad greens among four bowls. Top each with cooked ground beef, cherry tomatoes, cucumber, shredded cheddar cheese, avocado slices, and a dollop of the caramelized onion aioli.
Serve immediately and enjoy!