Dice the onion and tomatoes, chop the cilantro if using, and halve the lime. Cut the avocado in half, remove the pit, and scoop the flesh into a mixing bowl.

In a large skillet over medium-high heat, add the ground beef and break it up with a spatula. Cook, stirring occasionally, until fully browned and no longer pink, about 8 to 10 minutes. Drain excess fat if needed.

Push the beef to one side of the skillet and add the diced onion. Sauté until translucent and fragrant, about 4 minutes. Sprinkle in chili powder, cumin, paprika, garlic powder, salt, and pepper. Stir to combine and toast the spices slightly. Add a tablespoon of water or broth if the mixture looks dry.

In the mixing bowl with avocado, mash with a fork. Add sour cream, fresh lime juice, chopped cilantro, and a pinch of salt. Stir or whisk until smooth and creamy. Adjust lime or salt to taste.

Spoon the seasoned beef and onion mixture into bowls. Top with diced tomatoes and a generous drizzle or dollop of avocado crema. Garnish with extra cilantro or shredded cheese if desired. Serve immediately.