Last few times I cooked Costco chicken breasts:
1. Marinated chicken in a baggies with soy sauce, red pepper, black pepper, garlic powder, onion powder for an hour or so. Baked with french-fry-cut potatoes at about 350 degrees for 20 minutes or so until done.
2. Sliced chicken into bites, began to cook in wok with a little water, red pepper, and black pepper. Sliced onions, bell peppers, and jalapenos. When chicken was mostly cooked, added vegetables and cooked all together until chicken was done. Served with tortillas and refried beans.
3. Semi-baked two chicken breasts for a while. Made up a batch of Bisquik biscuit dough, and made four big flat patties. Removed chicken and placed on a pattie, added some pepper jack cheese and other spices, then covered with remaining biscuit patties, closed up the edges, and baked all together for 15 minutes at 425 degrees. I could only finish about half of one of these monsters in one sitting.
I'm not much of a cook, but this week I tried it a few times since teh wom0n was getting home late and I didn't want her to cook. All were successes, IMHO.