Those burgers aren't having any fun...
The item id for Burger in unturned is 6637. You can use this ID with the commands below to spawn the item, give it to a player or buy it on a modded economy server.
Useable: Consumeable
Size_X: 1
Size_Y: 1
Size_Z: 0.33
Food: 40
Blueprints: 1
Blueprint_0_Type: Supply
Blueprint_0_Supplies: 3
Blueprint_0_Supply_0_ID: 6636
Blueprint_0_Supply_1_ID: 340
Blueprint_0_Supply_2_ID: 460
Blueprint_0_Supply_0_Amount: 1
Blueprint_0_Supply_1_Amount: 1
Blueprint_0_Supply_2_Amount: 2
Blueprint_0_Level: 1
Blueprint_0_Skill: Cook
Blueprint_0_Build: 27
Blueprint_0_Product: 6637
Blueprint_0_Map: Easter