Being from San Diego, I fully agree that spicy food is very hard to find here. God, I miss Mexican food so much it breaks my heart. I can offer a couple suggestions -
Peruvian restaurants make spicy food. It will probably come to the table very mild, because they are accustomed to their Argentine customers crying like a little girl if it's even a tiny bit spicy, but you can ask. And they will usually have a squeeze bottle of a yellowish sauce that will seriously clear your sinuses if you use a generous amount.
There used to be a Peruvian place on Fitz Roy called El Peruanito Rey that was very good, but I haven't been there since before the plandemic, so I don't know if it's even still open. As a general rule, if there's a hugely fat Latina in the kitchen, the food is probably good.
There's also a tiny but very good Korean restaurant on Esmeralda (second block east of 9 de Julio) just north of Esmeralda. The name is Fan Fan Song, or maybe Fan Song Song. If you get your food to go it will be very mild, even if you asked for spicy, see the reason above. But if you eat there, and ask for hot sauce, they will give you a little dish with some evil red hot sauce that will cauterize your tonsils. I used the whole first dish and asked for more. Again, they are used to customers who think black pepper is spicy, so they may caution you elaborately about how hot it is, but just politely insist that you are American, not Argentino.