There's a new burger joint called Papachos on the corner of 28 de julio and La Paz in Miraflores. I tried it yesterday and it was delicious! Supposedly it's a new Gaston place but I'm not sure if it's actually his or they just paid for the name. Nevertheless, it's great!
They have about 20 different kinds of burgers and you can change any meat patty for a quinoa or veggie patty if you're vegetarian! I had a quinoa burger with provolone cheese, arugula, baby tomatoes and pesto mayo...lush! They also have really good onion rings and fries. Some of their other dishes looked good too like mac and cheese and hot dogs! A reason to go back.
They also serve Sierra Andina beer, the ex-pat craft brew from Huaraz.
It is definitely a little on the pricey side but totally worth it for the occasional splurge!