Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a large bowl, combine cornmeal, flour, baking powder, salt, and sugar. Mix well.
In another bowl, whisk together milk, vegetable oil, and egg until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
Spoon the cornbread batter into the prepared muffin tin, filling each liner about halfway.
In a skillet over medium heat, cook the ground beef until browned. Drain excess fat.
Add taco seasoning to the beef along with a splash of water. Stir and cook for an additional 5 minutes until well combined.
Spoon a generous amount of the seasoned beef mixture on top of the cornbread batter in each cupcake liner.
Sprinkle shredded cheddar cheese on top of the beef in each cupcake.
Bake in the preheated oven for 20-25 minutes, or until the cornbread is golden and a toothpick inserted comes out clean.
Remove from the oven and let cool for a few minutes. Top each cupcake with a dollop of sour cream, chopped green onions, diced tomatoes, and olives if using.
Garnish with fresh cilantro if desired and serve warm.