1. For the Marinade: Combine oils, garlic, ginger, soy sauce, sugar, red pepper flakes, scallions, salt, and pepper in large bowl. Add steak cubes and toss to coat evenly. Cover and refrigerate until fully seasoned, at least one hour or up to 24 hours.
2. Ignite 1 large chimney (about 6 quarts, or 5 pounds) of charcoal and burn until covered with thin coating of light gray ash, about 20 minutes. Empty coals into grill and spread over three-quarters of grill surface. Position grill rack over coals; heat until hot, about 5 minutes. Scrape rack clean with wire brush.
3. For the Fruit and Vegetables: Toss pineapple and peppers with 1 1/2 tablespoons vegetable oil in medium bowl and season with salt and pepper. Brush onions with remaining oil and season with salt and pepper. Using eight 12-inch metal skewers and following illustrations below, thread each skewer with a pineapple piece, a stack of onion, a cube of meat (skewering as if it were an uncut cube), and one piece of each kind of pepper, and then repeat this sequence two more times. Brush any oil remaining in bowl over skewers.
4. Grill kebabs directly over coals, uncovered, until meat is well browned, grill marked, and cooked to medium-rare, about 7 minutes (or about 8 minutes for medium), turning each kabob every 1 3/4 minutes to brown all sides. Transfer kebabs to serving platter, squeeze lemon or lime wedges over kebabs, if desired; serve immediately.
STEP BY STEP: Cutting the Kebab Meat
1. Halve each steak lengthwise, leaving gristle on one half.
2. Cut away the gristle from the half to which it is still attached.
3. Cube meat, and cut each cube almost through at center.
STEP BY STEP: Kebab Preparation: Onion
1.Trim ends from onion and peel away dry outer skin. Halve lengthwise. Peel and discard inner core.
2. Slice each onion half lengthwise into four pieces, then cut each piece crosswise into thirds.
STEP BY STEP: Kebab Preparation: Pineapple
1. Trim both ends of pineapple and peel. Halve lengthwise, reserve one half for another use, and halve remaining half lengthwise. Remove woody triangular core.
2. Cut each piece crosswise into six chunks.
STEP BY STEP: Kebab Preparation: Peppers
1. Cut away two wide planks of pepper on opposite sides of core, then cut away two remaining smaller sections.
2. Cut smaller sections crosswise into thirds. Cut each of the larger sections into nice pieces.
STEP BY STEP: Kebab Preparation: Skewering
A completed skewer has three repeating rows of vegetables, fruit, and meat, in the order illustrated.