Rinse flank steak or boned, skinned chicken breasts and pat dry. Slice diagonally across the grain into 1/4-inch thick strips.
In a zip-lock plastic bag (1-gal. capacity), mix 1/2 cup water, soy sauce, ginger, rice vinegar, sugar, and Asian red chili paste; add meat. Cover and chill up to 1 day, or seal and freeze up to 1 week ahead.
Buy 12-inch wooden skewers and peanut sauce.
Lift meat from marinade (discard marinade) and thread each strip on a skewer.
Grill over high heat (you can hold your hand at grill level 2 to 3 seconds), turning once, until beef is browned on the outside and still slightly pink in center or chicken is no longer pink in center (cut to test), about 5 minutes.
Serve with peanut sauce on the side.