Everyday we cook something and produce naturally decomposable wastes. For example unused chopped onions, potatos, tomatos, roots, or old food. This creates waste of 200-500 gram daily. I was thinking, how can we reduce this or recycle it to create some garden soil? What are the ways to reduce or recycle this kind of waste? I am already trying to use less plastic bags.
I'm going to focus my answer on 'recycling' the wastes and let someone else answer how to reduce kitchen waste.
If your municipality doesn't collect and process kitchen and garden wastes then you can start composting (a lot of) the kitchen waste yourself. Basically you have 3 options:
'Regular' composting: create a compost pile or setup a compost bin in your garden. It's easy to do, but with regular composting it will take a while before the wastes are fully decomposed and you have good compost. Also some materials are less suited to be placed on a compost pile, for example greasy foods and large batches of citrus fruits because that will slow the decomposition process down. Also meat is less suitable (see this question for an explanation).
Vermicomposting: this is similar to regular composting, but then you use a compost bin in which you put specific types of earthworms that speed up decomposition. The worms also excrete castings that improve the quality of the compost.
Bokashi composting: buy two airtight bins and start filling one bin with food scraps and a bokashi bran (bought in a store or made yourself). When the bin is full, leave it closed for 2-3 weeks to ferment all material. During this period you can use and fill your second bin. Once fermentation is done you can bury the waste in the ground for a few weeks so it turns into soil, or you can apply it slowly to a compost heap or wormbin. The main advantage is that you can process more materials (also cooked and greasy foods), but the drawback is that you'll need to buy or create new microorganisms regularly.
Another idea is to reuse your wasted veggies and turn them into the food source for more food for yourself. We own chickens, who will eat almost anything. Here is a good chart to figure out how to recycle your table scraps into food for something that in return provides food for yourself. There are several types of fish you can also grow in small(er) ponds (Google: Backyard Fish Farming). The best benefit of both is the soluble wastes of both make amazing fertilizer which is much easier to break down than the table scraps you've started out with.