When did cooking get assigned to women ?? It should have been a joint resposibility ,when we were hunter gatherers … 
Is it after the discovery of fire , that the roles got specific ??
( I am fully aware that men also do cook 
)…
It’s down to children.
Men hunted; women gathered and looked after the kids. You can gather food (berries, tubers, fruits, etc), prepare food, and cook, all while keeping an eye on children but you can’t hunt and do the same. And pregnancy’s a bit of a handicap for hunting too.
Yup. Women tend to get the jobs that mostly stay in one place and that can be easily interrupted. Working in fields, cooking, spinning, weaving, sewing, keeping the house running and so on are more easily done with needy children underfoot than hunting, sea fishing, marauding and so on. So women traditionally got them–especially since it was so much more common to nurse a child for a few years, and people needed to have a lot of children just to keep the population stable.
More like “social evolution,” though, unless someone can demonstrate selection for cooking.
I have no idea how young males would survive long enough to reproduce without pizza delivery and Taco Bell.
In my culture, cooking is prestigious and jealously competitive among the older, past child-bearing years women. I see this as a way to stay valued to the point of indispensability. Recipes and techniques are guarded fiercely and are a source of pride and envy. Cooking is seen as an art, not a chore.
Keep in mind that some parts and forms of cooking were are still are chiefly the domain of men. Butchering a large animal, for example, takes some brute physical strength. Roasting large animals, if you do it in large chunks, will also take physical strength to manipulate things like spits. Digging roasting pits likewise.
My (unscientific) observation is that men tend to capture/kill large animals and perform the initial butchery (skinning, gutting, jointing) with the women taking over when the lumps of meat become smaller and easier to handle.
When harvests are abundant (and gatherers will get seasonal abundance) both men and women will engage in processing the food.
Even if men don’t ordinarily cook day-to-day, in most cultures they remain capable of putting a meal together. In many, while home-cooking is the domain of women, the profession of cooking, that is, cooking-for-hire, belongs to men.
But all that said, even among hunter-gatherers, cooking tends to be women’s work. Because of all the above reasons listed in other posts.