In a large skillet (preferably cast iron) over medium-high heat, cook beef, stirring frequently, until browned, about 5 minutes. Drain and discard fat, leaving meat in pot.
Reduce heat to medium, then add tomatoes and cheese. Cook, stirring frequently, until cheese is melted, about 5 minutes. Remove from heat and stir in chili powder (if using).
Serve dip warm in skillet or a serving bowl. Top with cilantro (if using) and serve with chips alongside.