It would be a brave individual who made recommendations based on such scant information. Lisbon is packed with places to eat, some great some not so great. The choice kinda depends on your tastes and the depth of your pocket. I'd suggest you consult:

https://www.tripadvisor.co.uk/Restau..._Portugal.html
https://www.fodors.com/world/europe/...on/restaurants
https://www.timeout.com/lisbon/resta...on-restaurants
https://www.zomato.com/grande-lisboa

same applies to Porto. And I guess, just about anywhere else