In a medium saucepan, combine 1 cup of long grain white rice and 2 cups of water. Bring to a boil over high heat.
Once boiling, reduce heat to low, cover, and simmer for 15 minutes or until the rice is tender and water is absorbed. Remove from heat and let it sit, covered, for 5 minutes.
While the rice cooks, heat 1 tablespoon olive oil in a large skillet over medium-high heat.
Add the finely chopped onion and cook for 3-4 minutes until softened.
Add the minced garlic and cook for 30 seconds until fragrant.
Add 1 pound ground beef to the skillet. Cook, breaking it apart with a spatula, until browned and cooked through, about 6-8 minutes.
Drain excess fat from the skillet if necessary.
Stir in 1 tablespoon chili powder, 1 teaspoon ground cumin, 1/2 teaspoon smoked paprika, 1/2 teaspoon dried oregano, 1/4 teaspoon cayenne pepper, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Cook for 2 more minutes to let the spices bloom.
Add 1 cup drained black beans and 1 cup thawed corn kernels to the skillet. Stir to combine and cook for an additional 2 minutes until heated through.
In a small bowl, mix 1/2 cup sour cream, 1 tablespoon fresh lime juice, and 1/4 teaspoon salt. Set aside.
Fluff the cooked rice with a fork and divide evenly among 4 bowls.
Top each bowl of rice with the seasoned ground beef mixture.
Sprinkle 1 cup shredded sharp cheddar cheese evenly over the beef mixture.
Add diced tomato, sliced avocado, and chopped fresh cilantro on top of each bowl.
Drizzle the lime sour cream sauce over each bowl before serving.