Comment 7 by Alan4discussion :

It is quite probable that early man ate naturally cooked food (as animals do today) from those burned in natural bush fires in dry areas.

It is also probable that in selected volcanic locations fires would start naturally or could be started simply by putting dry sticks into hot volcanic ground, as in the 4th photo on the link.

After you arrive at the visitors Car Park you will witness several demonstrations of 'how hot' the area is (temperatures just a few metres below the surface reach between 400°C and 600°C). Dry brush thrown into a hole in the ground catches fire immediately, while water poured into a bore hole erupts seconds later in the form of steam - like a mini-geyser.

Isn't it quite probable that the first cooked food that early man ate on a regular basis would have been prepared by immersing raw meat into hot springs - boiling it rather than broiling it?

Naturally occurring volcanic springs would have provided a much more reliable and permanent source of heat and wouldn't have required him to sit around twiddling his opposable thumbs waiting for a forest fire or a lightning strike to occur.

By the time our primitive ancestors (a relative term, I know) finally learned how to harness fire, they may already have been eating cooked food for thousands of years.