Once you try cooking with ketchup (we’re betting you’ll love it), play around some: Cook peanuts with the chicken, toss some slivered scallions in at the end — the color contrast is brilliant — or substitute soy sauce for the salt. Other proteins you can use: squid, shrimp, tofu (if you’re using tofu, use firm or extra-firm; cut it into 8 slices and lig…