What additional ingredients and steps to take to make fast cooking oatmeal from oats?

I use large flake oats. Two-to-one by volume tap water to oats in a bowl. Don't even stir, you'll have to do something with the wet spoon if you do. Handful of dried raisins and/or cranberries. Microwave for 2 minutes at 70%. Add a few shakes of salt (salt is really important for oatmeal) and give it a good stir. When you take it out of the microwave it will look done, but stirring will reveal there are less cooked oats under the ones at the top.

Give it another 2 minutes at 70 and stir it well again. I often stir in a little milk at this point, which can cool it as well as making it creamier. If you find you would like it sweeter, a little brown sugar or maple syrup over the top and not stirred in work wonderfully.

If instead of large flake you have quick oats, you'll need less time in the microwave. Instant oats need only boiling water, but they generally only come pre-flavoured and sweetened. If you did get plain instant, you'd probably want to cut your dried fruit small so it would be ok with just boiling water. Steel cut oats need significant cooking - most people I know use a slow cooker over night. If you're not sure what you got from the bulk store, either experiment with different cooking times until you're happy, or look for pictures of various oat forms until you know what you have.

Instant porridge/oatmeal normally has milk powder added to par-cooked oats. Non-instant porridge normally uses milk. You can make a water porridge, but soaking is good for most oats if you're going to do that. The exact method will depend on what sort of oats you have, but you will need to simmer for a few minutes at a minimum.

If you want a handy shelf-stable preparation my camping recipe works well: 60g of rolled oats, 30g of milk powder, 1 tsp sugar, and any dry flavourings you like (cinammon, dried fruit...). Add 350-400ml of hot water, bring back to the boil, turn down heat and cook until done. I actually turn the heat right off for about 10 minutes and cover/wrap in a towel, to save camping fuel and because my stove is rather fierce, before finishing off over the heat. This can also be microwaved in a large bowl - 2 minutes on high, wait a few minutes, 1 minute on high, repeat the wait/1 minute part until ready.