In a large skillet, heat olive oil over medium heat. Add diced onion and sauté until translucent, about 3-4 minutes. Add minced garlic and cook for an additional minute until fragrant.

Add ground beef to the skillet, breaking it apart with a spatula. Cook until browned and fully cooked, about 6-8 minutes. Drain excess fat if necessary.

Stir in taco seasoning and water, mixing well. Bring to a simmer and cook for about 5 minutes until the mixture thickens. Remove from heat and let cool slightly.

In a large bowl, combine chopped romaine lettuce, cherry tomatoes, black beans, corn, and half of the shredded cheddar cheese. Toss to mix.

Divide the salad mixture among serving bowls. Top each with the seasoned beef, diced avocado, remaining cheddar cheese, sour cream, salsa, and fresh cilantro.

Season with salt and pepper to taste. Serve immediately.