Brown the ground beef in a large skillet over medium-high heat, breaking it up, until no longer pink, 6 to 7 minutes. Drain off all but about 1 tbsp of fat. Add the onion, garlic, chili powder, cumin, smoked paprika, salt, and pepper. Cook until the onion softens, 3 to 4 minutes.

Pour in the water and scrape up any browned bits from the pan. Cook until the liquid evaporates, 1 to 2 minutes, then remove from the heat.

Lay a tortilla flat. Sprinkle ¼ cup of cheese over half the tortilla, top with about ½ cup of the beef filling, then scatter another ¼ cup cheese on top. Fold the tortilla over to form a half-moon. Repeat with the remaining tortillas and filling.

Wipe out the skillet and return it to medium heat. Place one folded quesadilla in the dry pan and cook until the underside is deep golden, 2 to 3 minutes. Flip and cook the other side until golden and the cheese melts, another 2 to 3 minutes. Transfer to a cutting board and repeat.

Let the quesadillas sit for 1 minute, then slice into wedges. Serve hot with sour cream and salsa.