Heat olive oil in a heavy pot, sauté chopped onion and garlic paste until soft.
Add ground beef, cumin powder, oregano, salt, and water; simmer on low heat for 30 minutes until moisture evaporates completely.
Let the beef fry in its own rendering fat until crispy edges form.
Warm tortillas on a griddle.
Serve crispy carnitas beef inside warm tortillas with lime juice and diced onions.