Try to work with MoP classic

TillerTracker.lua

@@ -375,9 +375,25 @@ function TillerTracker:AllReputationsDone()
 	return true
 end
 
+function TillerTracker:GetAllCompletedQuestIDs()
+	if C_QuestLog.GetAllCompletedQuestIDs then
+		return C_QuestLog.GetAllCompletedQuestIDs()
+	elseif GetQuestsCompleted then
+		local completedQuestIds = {}
+
+		local questsCompleted = GetQuestsCompleted()
+
+		for quest_id in pairs(questsCompleted) do
+			table.insert(completedQuestIds, quest_id)
+		end
+
+		return completedQuestIds
+	end
+end
+
 function TillerTracker:UpdateData()
 	-- Get information on all quests completed
-	local questsCompleted = C_QuestLog.GetAllCompletedQuestIDs()
+	local questsCompleted = TillerTracker:GetAllCompletedQuestIDs()
 
 	-- Create a table to store our current inventory of required mats	
 	local inv_table = {}

TillerTracker.toc

@@ -1,6 +1,6 @@
 ## Interface: 110205
 ## Title: Tiller Tracker
-## Version: 11.0.1
+## Version: 11.0.3
 ## Notes: Helps with the daily Tiller food quests ("A Dish for...") by keeping track of what quests have been completed that day, how many dishes need to be cooked, and what materials are required.
 ## Author: Amanoa
 ## SavedVariables: TillerTrackerDB