Cut meat into 1-inch cubes and put onto a serving plate.
To make the Mexican sauce, heat the oil in a saucepan; add onion and garlic
and cook gently until softened.
Stir in tomatoes and their juice, tomato paste and chili powder. Simmer
uncovered for 10 minutes.
Remove the sauce from the heat and puree in a blender or food processor
until smooth or press through a sieve to give a smooth sauce. Return to the
heat. Add the chopped chile and simmer for 15 minutes more.