In a large skillet or pot, heat the olive oil over medium heat. Add the diced onion and sauté until translucent, about 3 minutes.

Add the ground beef and sprinkle with taco seasoning. Cook until fully browned, breaking the meat into crumbles. Drain excess grease and set the beef aside, leaving a thin layer of drippings in the pan.

In the same pan over medium heat, melt the butter. Whisk in the flour and cook for 1-2 minutes to form a light roux.

Slowly pour in the milk while whisking constantly until smooth and slightly thickened.

Stir in the Rotel (with juices). Reduce heat to low and gradually add the shredded cheddar, stirring until melted and creamy.

Stir in the sour cream and hot sauce (if using). Season with salt and black pepper to taste, and add extra taco seasoning if desired.

Add the cooked beef and onions back into the cheesy Rotel sauce and stir well to coat. Simmer on low for 8-10 minutes until thick, smooth, and scoopable.

Warm the flour tortillas in a dry skillet or microwave until soft and pliable.

Spoon the cheesy beef mixture into each tortilla. Garnish with diced tomatoes and chopped cilantro, then serve immediately while warm and creamy.