1/4 cup dry bread crumbs
1/4 cup finely chopped onion
1 1/2 pounds lean ground beef
1 (1 1/4-ounce) package taco seasoning mix
1 (7- to 8-inch) round loaf unsliced bread, sliced in half horizontally*
Sliced pitted ripe olives
Heat gas grill on medium or charcoal grill until coals are ash white.
Meanwhile, combine all hamburger ingredients except bread and butterin large bowl ; mix well. Shape into 1 large (8- to 9-inch) patty. Place onto waxed paper-lined baking sheet. Cover; refrigerate at least 30 minutes.
Meanwhile, spread bread halves with butter; set aside.
Place patty onto grill. Grill, turning once (if necessary, use two metal spatulas), until internal temperature reaches at least 160°F. (13 to 15 minutes). Place cheese on patty; continue grilling until cheese is melted (2 to 4 minutes).
Meanwhile, place bread halves, cut-side down, alongside patty (not directly over coals). Grill bread, rotating occasionally, until toasted (3 to 4 minutes).
To serve, place hamburger on bottom bread half; top with lettuce, tomato, olives, sour cream, guacamole and salsa. Top with bread half. For easier serving, skewer with 6 skewers from top to bottom. Cut into 6 wedges.
*If loaf of bread is too tall, slice into 3 horizontal layers. Remove center layer for other use.
If desired, jumbo burger can be made into 6 individual patties, using 6 slices cheese and served on 6 hamburger buns. Shape hamburger mixture into 6 patties. Place patties onto grill. Grill, turning once, until internal temperature reaches at least 160°F. (12 to 15 minutes). Top each with cheese. Continue grilling until cheese is melted (about 1 minute). Toast buns and serve as directed above.