Preheat your oven to 375°F (190°C).
In a large skillet over medium heat, add your ground beef. Cook until it’s browned, breaking it up with a spatula as it cooks. Drain any excess fat.
Stir in the taco seasoning and water. Add the undrained can of diced tomatoes and green chiles. Mix well and let it simmer for about 5 minutes until the mixture thickens slightly.
In a large mixing bowl, combine Bisquick and shredded cheddar cheese. Mix until the cheese is evenly distributed throughout the flour mixture.
To the dry ingredients, add the nacho cheese soup and buttermilk. Stir until just combined; do not overmix.
Gently fold the beef mixture into the batter until evenly distributed. The mixture should be thick and cheesy.
Grease your muffin tin or use muffin liners. Fill each cup about 2/3 full with the muffin batter.
Place the muffin tin in the preheated oven and bake for 18-20 minutes or until the tops are golden brown and a toothpick inserted in the center comes out clean.
Once baked, let the muffins cool in the tin for about 5 minutes before transferring them to a wire rack. Enjoy warm or at room temperature.