How to cook?

Go preferentially raw.

First you can and should eat a lot of food raw. It's delicious and nutritionally optimal because we need more vitamins, phyto-nutrients and all micro-nutrients than calories because of food abundance and low micro-nutrient content of farmed veggies and meat .
Our ancestors needed more calories to survive in food scarcity while the micro-nutrient of wild food is high.

Cook at low temperature

You need some time and some tools. Time is planning. Tools are not expensive but you need them.
Steam cooking is well done with an open system in order to avoid barometric trauma to vitamins and other fragile molecules. 

Oven cooking is the most reliable if you use a thermometer.

Junk oven are set to deliver high energy and cost a lot in electricity or town gas... You need an oven with low temperature settings.
The best is to buy a temperature controlled oven. It is expensive.
But you also need a pot and a Romertopf like casserole (meat brick) is perfect.