I had lunch here on a weekday, which is a pretty quiet time in Bellavista when many restaurants are closed. The hotel concierge recommended Azul Profundo, which our ski guide had also mentioned as having good seafood. We got one of the few window tables looking out onto the colorful street scene, which was nice.
The menu (bilingual) has various ceviche offerings and around eight types of grilled fish with four choices of sauces to accompany them. The server could not speak English but the lady at the bar quickly stepped in to handle our order and spoke very fluently. She recommended an octopus ceviche which was sprinkled with shredded cheese and came with an olive caper dipping sauce - it was interesting though we liked it better with the nice pico de gallo that accompanied the bread. The salmon ceviche was average. I had a very nice grilled tilapia with the caper/butter sauce though. We received excellent service, unlike some TA reviewers. I wouldn't say this is a must-go in Santiago, but if you are in the area and in the mood for fish it is a reasonable choice.