Question: What percentage of restaurants in Monterey County have Mexican food?
SQL: SELECT CAST(SUM(IIF(T2.food_type = 'mexican', 1, 0)) AS REAL) * 100 / COUNT(T2.id_restaurant) FROM geographic AS T1 INNER JOIN generalinfo AS T2 ON T1.city = T2.city WHERE T1.county = 'monterey county'