For marinade, trim ends of lemon grass; halve lengthwise. Remove two or three layers of tough outer stalk. Remove tender inner stalks; wrap, refrigerate, and reserve to garnish grilled steaks. Finely chop 1 tablespoon remaining lemon grass. In bowl combine chopped lemon grass, soy sauce, hoisin sauce, lemon juice, garlic, and crushed red pepper. Transfer 1/2 cup marinade to airtight container; refrigerate.
Place steak in large self-sealing plastic bag set in shallow dish. Pour remaining marinade over steaks; seal bag. Refrigerate 12 to 24 hours; turn occasionally.
Remove steaks from marinade; discard marinade. Let steaks stand at room temperature for 30 minutes.
For charcoal grill, place pineapple slices, nectarines, and plums on rack over hot coals. Cover and grill 4 to 6 minutes, until fruit is lightly seared, turning once. Brush with refrigerated marinade the last 2 minutes of grilling. Transfer fruit to platter; set aside.
For charcoal grill, place steaks on rack directly over medium coals. Cover and grill 15 to 18 minutes for medium rare (145 degrees F); turning once and brushing with refrigerated marinade the last 2 minutes of grilling. Place green onions on rack over coals; grill, uncovered, 1 minute, turning occasionally. (For gas grill, preheat grill to medium-high. Place fruit on rack over heat. Cover and grill fruit. Reduce heat to medium. Grill steaks and onions as above.)
Slice steaks. Serve with fruit, onions, and reserved lemon grass. Serves 4.