You have all these beautiful fruits, veggies, seeds, nuts and whole grains to prepare, do you have the ingredients that will provide the optimal nutrition as well? I am not a scientist, but I will try and explain this to you the best way it's been explained to me.
First thing to know is about cooking oil. Polyunsaturated fats (safflower, canola, vegetable oils, etc.) have only been around since the industrial revolution. They are highly processed and start to degrade at a very low temperature, even as much as the introduction of sunlight will effect the stability of the structure.
Fats are made up of chains of carbons; all 'saturated' by hydrogens. The more missing hydrogens there are any carbon in the chain, the less saturated the oil is and the weaker the chain. The carbons want to be saturated by hydrogens so in their not, the fat chains will pull hydrogens from wherever they're available. Adding heat to the already unstable chain will release more hydrogens in that process thus leaving more carbons to saturate. Now consume the unstable chain and where do you think the chain will be pulling the hydrogens from? Your body. If there is a missing hydrogen in your body (likely will be coming from major organs) this leaves space for anything else to bond to the available bond. This describes 'free radicals'.
So, let's talk saturated fats; organic coconut oil and animal fats are the highest saturated chains. They also hold their chemical structure at the highest temperature of all fat chains. Because consuming animal products provokes a whole other set of nutritional problems, organic coconut oil is the optimal oil for cooking. Coconut oil should not be heated over 295ºF. Slow cooking at a low temperature is the best option. My second choice would be ghee, but I personally choose plant-based because of the ease of digestion.
Other oils can be totally safe to consume as long as they're not heated. The benefits of olive oil are wonderful and I use organic olive oil, organic sesame oil to add to dressings and cold-prepared dishes. Another technique to change up the flavor would be to dry roast veggies and toss the oil in after they're cooked.
If you'd like to go further down the rabbit hole, you might want to take a look at some of Dr. Hyman's work. I really like the way that he explains the importance of cooking with coconut oil.