You can buy a lot of vegetarian burgers, saucages etc. in almost every supermarket. The best-known brands are Tivall, Quorn, Valess, Vivera, Planet Green. You'll find them in the refrigerator next to the fresh meat.
You can also find the tofu over there (or in some supermarkets at the vegetablesection).
Willemk49 just mentioned two shops with healthfood, one of them in the Gekingestraat and the other in the Boterdiep (the names of the streets).
I personally would recommend Quorn, escpecially the bits in peanutsauce ("Saté-stukjes), tastes very good with rice. And I use the "Tofu Roerbakreepjes" a lot, it's prepared tofu.
You just have to try some things, so you can find out what you like!