Most efficient plant?

So we have been living here for almost 2 years now, and I've always wanted to grow my own veges. So when we moved in I slowly started getting more and more and adding to the garden. At the moment we have a 2metre tall tomato/tamarillo tree that is about to start its first crop (only 6 on there) but it has taken a good year and a half to get to where it is. I planted carrots about 6 months ago and now they are wonderful, I dig them up as I need them and we always have plenty.
But the best plant we have at the moment would have to be our capsicum. It has been producing about 3 a week for pretty much all of this year(not counting the ones eaten by bugs) So I no longer need to buy them or the carrots.
Other trees we are trying to establish are: Orange tree (which has not seemed to grow for quite some time now but its still alive), Lemon tree, strawberry guava, Strawberries, Gooseberrys, Kiwi, passionfruit, nectarine, chilli's, onions and plenty of herbs (which are all fabulous and well established now) Most of the trees have been planted for at least a year, we are just waiting for them to grow. The Kiwi tree was one plant that was here when we moved in and still has not had fruit (there is def a male & female!) We think next year we will see fruit from it.
I'd like to know what other veges/fruit other bb members grow that seems to produce alot of produce and is a worth while plant? Plus any tips to help them produce fruit/veges a little faster?
I'd deffinantly reccomend everyone had a capsicum (if they like them) as they are so hardy and produce well!

Some fruit trees just take a little longer to start producing than others, citrus tends to be a bit slower than some of the summer stone fruits, for example. One tip is to shop at a good nursery and speak to the nurseryman about which varieties are better locally suited & which will bear fruit sooner. Often you can buy trees that are a year or two older but they cost a little more.

Re veggies, we have found zucchinis to be very prolific - so much that we've had far too many in past years, and have cut back to only having one or two bushes each summer. Pumpkins are also good if you have space and get them into the ground early in spring, smaller varieties like butternut and jap are good if winter arrives early, the big ones may not get ripe before the frosts. Another excellent crop if you have the room is potatoes, they grow bazillions of potatoes and you can start harvesting early for little new potatoes and also leave some in for bigger potatoes later in the season. Good value too in that you can replant some of them for the following years so the crop keeps renewing itself, kwim.

Thanks! I tried zucchinis last year and I got one, then it died :( I think it must have been in the wrong area though. Pumpkin is a good one too.. my mum has that one and it runs along her fence line for about 10 metres! Crazy! I dont think I'd have the room for it though. I think I will try zucchinis again this year.
There is just something wonderful about growing your own veges. Our carrots taste so fragrant, they have.. flavour unlike the ones you'd buy at the shops. Potatoes were here when we got here, and we somehow managed to get rid of them all because they were taking over the whole garden. I think to put them in a pot would be best yeah?
The citrus tree's, our neighbour told us that if you pick off the flowers, then it will encourage it to grow because it wont put all it's effort into trying to produce fruit rather than growing. So we're trying that, but we porbably should talk to the nursary people about it as it doesnt seem to be helping..

Poopie I remember the old mob on Gardening Australia used to talk a lot about using ?superphospate? when you plant things because it gives the root growth a really good burst, as well as lots of seaweed liquid stuff because that encourages all the healthy plant enzymes. Perhaps with the zucchini you planted it too early or late...they really don't cope in the cold weather, strictly for spring-summer. I think you're just going to have to wait for the citrus, we planted a mandarine 6 years ago and to our knowledge this will be the first year we'll have fruit off it (I think the tenants didn't water over summer so it's a hardy little thing) :)