This place has the best tuna (carnitas de atun) tacos EVER. If you don't think that sounds appealing, come here to change your mind. Also passionfruit limonada. Or berry. My husband always gets the ballena.
It can be crowded and like most places of its type in Guadalajara, it doesn't stay open late (maybe 5? if you're lucky?) but if you can come at US lunchtime instead of Mexican comida, you should be good.
This is on the corner of Morelos and Progresso, near Chapultepec and Hidalgo.