I seem to remember you said you were relatively new learner. So, before giving an answer and addressing the example you give, perhaps I should say that your question touches some of the most difficult but ultimately unavoidable parts of Japanese grammar to grasp if, like me, you are not a linguist and studying Japanese is the first time you have had to understand the difference between say a transitive and intransitive verb.
I have given a set of sentences below which illustrate the difference between てある、ている、〜た and the past forms but it sounds like the most important thing is to understand てある, which is hopefully illustrated but the following two sentences:
ビールを冷やしてある | The beer has been chilled.
ビールが冷えている | The beer is chilled.
The important point to grasp is that although both sentences accurately describe the current state of the same bottle of beer,
the first sentence, which uses the transitive verb + てある, tells us that the beer was at one time "warm" (which is not unusual in my country, the UK, where we are famous for drinking our beer warm) but, someone took action and chilled it.
In the second sentence the intransitive verb is used and we are told the beer is chilled but we are not told if it was ever warm or if somebody took steps to chill it.
Also, as pointed out by someone else, the 〜てある form is not used with intransitive verbs.
Now, if you understand the difference between transitive and intransitive verbs and everything covered so far in this answer then I would say we've covered 90% of your question and only the hardest 10%, which requires you understand the nuances of the 〜ている form, remains.
This is explained very well in the paper recently cited by Snailplane, "A Study of "V-te iru" in Japanese by Taeko Tomioka" but as this can take sometime and I think you said you were a beginner, it might be tactically sensible to;
(1) learn and practice using the examples of transitive/intransitive pairs & 〜てある given in your text book and
(2) go through the examples below and when you have time return to the paper or take a look at some of the other related questions on this site.
Example sentences to illustrate the difference between てある、ている、〜た etc
[explanatory comments are in sq. parentheses]
ビールを冷やす | I (will) chill the beer. [plain / future]
ビールを冷やした | I chilled the beer. [past, perfect]
ビールを冷やしてある | The beer has been chilled. [by me or another undisclosed person]
ビールが冷えている | The beer is chilled. [subject has changed (= Resultative state)]
And then, (そして);
ビールを暖める | I (will) warm up the beer. [plain / future]
ビールを暖めている | I am warming up the beer. [Progressive / Continuative state]
ビールを暖めた | I warmed up the beer. [past, perfect]
ビールが暖めてある | The beer has been warmed up [by me / someone]
＝＞ As a result (その結果)
ビールが冷えたが 今、 | The was chilled but now,
もう冷えていない。 | it is not chilled anymore.
Your example
Finally, let's apply this to the example you give:
昼ごはんを作ってある | My dinner has been prepared (~made)
昼ごはんを作った | I prepared (~made) my dinner.
In the first sentence we are told somebody prepared your dinner but not who (although you may be able to infer this from the context). In the second sentence we are told that you prepared your dinner (past).
If you have grasped the nuances of the 〜ている then you might infer from the first sentence that your dinner was ready and waiting to be eaten but not from the second sentence which just states somebody prepared it (past tense).
(Note: If you wanted to emphasize to somebody that you had prepared your dinner and it was now ready and waiting to be eaten and for some reason you did not want to use the 〜てある form, then you might say 「僕が昼ごはんを作っているけど・・」but before going there it might be better to study the 〜ている further.)
Additional note:
I have just noticed my first two sentences are also used by Hanaoka McGloin in "A students' guide to Jse Gmmr". She tells us that:
"[The first sentence] could be used when one is having a party and tells a friend that beer has been chilled and is ready to go. A wife, on her husband's return, on the other hand, could utter either [sentence]. In such a case, the difference is a matter of focus. The [first sentence] would imply that the beer was especially done for him. [The second] on the other hand, states the fact matter-of-factly."
