Do I have to defrost chicken before cooking?

Not a great idea. The oven cooks from the outside in, so by the time your chicken is done on the outside, it'll still be uncooked on the inside. If you cook it longer so it cooks through, the outside will be as tough as shoe leather and the inside will be just lukewarm enough to encourage microorganisms (that may have survived the freezer) to fester, which could sicken you.

Put it in the pan the night before, cover it (or not, as Alton Brown sometimes suggests), and put the pan in the refrigerator. When you get home from work or whatever, preheat the oven to 450 F, season it, and bake until done. When is it done? It's done when:

The chicken is done when an instant-read thermometer reads 165 degrees F when inserted into the thickest part of the thigh (the legs of the chicken should wiggle easily from the sockets too.) Remove the chicken to a platter and let stand for 10 minutes, so the juices settle back into the meat before carving.

http://www.foodnetwork.com/recipes/tyler-florence/the-ultimate-roast-chicken-recipe/index.html

Note that some would say 165 F is over done, but safe is better than losing a kidney to E. coli or other nasty microbeasties.

Since you mentioned the chicken tenders instead of a whole chicken it's easier to give a more appropriate answer now. Chicken tenders have much less mass and more surface area than the whole chicken, and because of that they thaw faster.

I have, before, cooked frozen chicken breasts and tenders by adding the frozen chicken to a cold, lightly oiled pan. Add water to come halfway up the chicken, cover the pan and cook on a medium-low heat for 15 minutes or so. Then turn the heat up slightly and uncover the pan to boil the water off and brown the chicken.

I've cooked from frozen to the pan as long as it just the chicken flats (thin cuts of chicken breast). It's kind of like throwing a frozen hamburger patty in the pan.

When you get to thicker meats, it is a problem. When the outside is done, the inside is still raw. I wouldn't do whole chicken breasts in the pan frozen or even a steak. Take the time to either pull it out and defrost or throw in the refrigerator the day before.

On my cooking show I always recommend bringing all meat to room temp before seasoning, marinating and cooking.

I put them in a toaster a couple of times. It seems to work.