Heat a large skillet over medium heat.
Add ground beef and chopped onion, cooking until the beef is browned (about 5 minutes). Drain excess fat.
Stir in diced tomatoes, water, rice, and taco seasoning.
Bring the mixture to a boil.
Reduce heat to medium-low, cover, and simmer for about 25 minutes until the rice is tender.
Remove from heat and sprinkle cheese on top.
Let the cheese melt, then top with shredded lettuce before serving.
This Easy Taco Skillet is best served hot straight from the pan.