I think adding pizzas and pies would be a nice addition, not only because it is something new to the game, but also because it could add a different curve to pking methods and monster killing methods. I'll start off explaining pizzas.
Pizzas can only be made with a pizza base, which requires water and flour, these shouldn't be hard to obtain as there are many areas to pick wheat and a lot of wells to obtain flour. However, the wheat has to be turned into flour through the mill, and I checked and the Mill in Lumbridge isn't working, so that would need to be fixed as well as the other mills (i'm assuming). If we wanted to make it a little easier would could just add flour into the general store, which I think would be a smarter suggestion. Once you have the flour and water just combine the two into a pizza base, which will require you to have a tin. I think this tin should be purchasable in the Cooking Guild located just South West of the Grand Exchange. Once the pizza base is in the pan you can simply cook it over a fire or skillet and get a regular pizza. The cool twist about pizzas is that you can add toppings. The toppings you can add are meat, Anchovy, and Pineapple. Pizzas have two halves which each health the same amount. Pizzas also require a tomato and cheese to make, but I think that should be something that we leave out.
Meat pizzas: You can either put cooked chicken or cooked meat (obtained from cows)on top of the pizza base in the tin. These will heal 18 hitpoints (9 heath each slice) This will require 30 cooking.
Anchovy pizzas: Simply you put an anchovy on top of the pizza. Anchovies can be caught by a small fishing net in Mudksipper point, Catherby, or Rimmington. Anchovy pizzas will heal 20 hitpoints, 10 hp a slice. This will require 35 cooking.
Pineapple Pizzas: Personally my favorite. Pineapples can be found in the picture below. Once you get pineapple you will have to slice them in to pineapples rings or chunks, your choice. These would heal 24 total, 12 hp per slice. This will require 85 cooking. I understand these will heal more than Mantas, but that will also mark the price up on them significantly.
http://imgur.com/delete/QGizqRmQMd5Mz9v
Now to talk about pie because who doesn't like pie?! Pies are made the same way as a pizzas is, you need flour and water to make pastry dough, then use the pastry dough on a pie tin, which can also be bought from the Cooking guild, then you can make a plain pie or add toppings too it. Pies also have two portions, requiring two bites each. The pies that should be added in are as followed.
Meat Pie: You can use either chicken or meat to make this pie also. It will heal 18 hitpoints, 9 hp a slice. This will require 30 cooking.
Fish Pie: You can add either pike or salmon to this pie, they will both heal the same amount equivalent to 10 hp per slice, for a grand total of 20 hp. This will require 35 cooking.
Admiral Pie: By adding either a monk fish or or shark you can make this pie. This will health 11 hp per slice, 22 all together. This will require 82 cooking.
This last pie is something that would be custom, I think it could be interesting to see if players use it or not it will simply be called a
Manta Pie. As said in the name, you'll need a manta ray. This pie will heal 13 hp per slice, for a total of 26 hp. This custom pie could be a success, or it could not. Just a hit and miss thing. This will require 92 cooking.
I've changed the hp of all the pizzas and pies from OSRS. I've also changed the required level a little bit. Here is a link that you can refer to if you have any further questions of information that I accidentally left out. I'm not sure how much more useful it will be since I changed it so much, but it can't hurt to offer the link.
http://2007.runescape.wikia.com/wiki/Cooking