Should I press the chicken breast against the pan when I grill it? When I'm about to grill a chicken breast, I usually cut the breast in very thin pieces. I put some oil in a square grill pan (exactly like this one) and turn on the stove (in a very high temperature). After a few minutes, I spread the oil, turn the temperature in medium and put the breast chicken there. I usually wait until the side of the chicken that I'm looking is almost completely white. Than I turn the slice.

My cousin is a chef, so he knows a lot about food. When I said that I pressed the breast chicken against the pan, he said to me not to. He told me just to leave the slice there and, when there's a lot of water in the side of the piece that I'm looking at, then it's the time to turn it. I tried this, but the other side of the chicken is never beautiful as the part that was against the pan. Than I kinda freak out and start pressing with the fork again, afraid that I might eat a raw chicken - wich stinks!

Can you guys give me some advice? I read a lot about it on the Internet and here, tried a lot of things, but most of the advice and recipes didn't work. I'm using only salt and olive oil to marinate the chicken breast (and the oil that I put in the pan). Since I'm on a diet, I can't use sauces that are not 'natural' (like italian sauce, sold in the supermarkets).

Sometimes I believe there's something wrong with the size of the pan, considering the size of the stove burners (maybe the pan is too big for it?). Does that have some impact?
The only method I have personally found to be reliable for grilling/pan-frying chicken breasts to a relatively uniform doneness is to pound them very, very thin with a mallet or rolling pin. Thin, as in scaloppine-thin, so that it cooks almost instantly in the pan.

Every other stovetop-only method is almost certainly going to produce a bland, tough cut, regardless of whether you press it down or not. As noted in my comment, my usual (lazier) method that does not involve pounding is to get a nice sear in the pan, then jam in a temperature probe and bake it in the oven until it's done (the USDA recommends 165° F, I usually don't go quite that high).

If pressing the meat actually accomplishes anything at all, it would most likely be to just squeeze out whatever tiny amount of precious juices the breast does have, and possibly give you slightly more even cooking on the exterior only; it will not help to cook the interior much faster unless, as stated above, the cut has been pounded extremely thin and flat, at which point it doesn't really matter.

P.S. Salt and olive oil is a terrible "marinade" for any cut of meat, especially a chicken breast. The salt is just going to get suspended in the oil and never reach the meat at all, and the oil itself won't have much of an effect on such a lean cut. You really need to change your marinade as well, preferably to something water-based (or at least not 100% oil).