1 tablespoon olive oil
1 small onion, finely chopped
1 lb ground sirloin
2 tablespoons low sodium Taco seasoning
8 ounces processed American cheese (such as Velveeta®), cut into large chunks
1 (10-ounce) can diced tomatoes with green chiles (such as RO*TEL®)
8 to 10 crunchy taco shells
shredded iceberg lettuce
toppings of choice such as diced tomato, hot sauce and sour cream (optional)
Heat oil in a large skillet over medium-high heat. Add onion and cook 1 minute, stirring constantly. Add ground beef and cook, crumbling with a wooden spoon until browned and cooked through, 5 to 10 minutes. Add in taco seasoning and cook for 1 minute. Mix in cheese and tomatoes and reduce heat to medium-low. Cook stirring constantly, until cheese is melted and mixture comes to a simmer. Cook for 3 minutes and remove from heat.
Add filling to taco shells and top with shredded lettuce and other toppings, if desired.