I'll let you in on a secret- if you get turned away from the more upscale sushi joint GoJuu down…read morethe street, you'd find yourself lucky to walk into AronSushi instead. Authentic, no frills, down-to-business sushi at AronSushi made by Portuguese chefs. I went for lunch but didn't order a lunch special; instead I indulged in selecting my own nigiri pieces, and the toro, chutoro, and o-toro were like heaven.
The chefs are efficient (my nigiri came out quickly!) and the service was impeccable. The server asked me if I preferred room temperature water or cold, and she was quick to take my order. She also made sure to check if I wanted the wasabi incorporated into the nigiri (yes, of course I do!), and in general it was a delightful experience.
For people who are traveling, there is are serene park nearby and the Museu Calouste Gulbenkian, so you can make a nice trip to this area of town.