In a large skillet, heat olive oil over medium heat. Add the diced onion and cook until softened, about 3-4 minutes. Stir in the minced garlic and cook for an additional 1 minute.

Add the ground beef to the skillet, breaking it apart with a spatula. Cook until browned and cooked through, about 5-7 minutes. Drain excess fat if necessary.

Stir in the taco seasoning and water. Bring to a simmer and cook for about 5 minutes, until the mixture thickens. Season with salt and pepper to taste.

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

Top the salad mixture with the cooked beef, remaining cheddar cheese, diced avocado, sour cream, salsa, and chopped cilantro.

Toss gently to combine all ingredients. Serve immediately or chill in the refrigerator for 30 minutes for a cooler salad.