Preheat the oven to 375°F and line a baking sheet with parchment paper.
In a large bowl, combine the ground beef, taco seasoning, 1/2 cup of the cheddar cheese, breadcrumbs, egg, and diced onion. Mix until evenly blended.
Divide the mixture into eight equal portions and shape each into a small loaf. Place the loaves on the prepared baking sheet.
Bake for 20 minutes, then sprinkle the remaining 1/2 cup cheese over the tops and return to the oven for 5 more minutes until the cheese melts and the internal temperature reaches 160°F.
While the meatloaves bake, mash the avocado in a medium bowl with the lime juice and a pinch of salt. Stir in the cooked rice and chopped cilantro until well combined.