Step 1 Slice garlic with sharp knife into about 5 slices lengthwise. Make a pile of slices and cut through them lengthwise again, then crosswise to mince. Set aside.
Step 2 Whisk together garlic, mayonnaise, brown sugar, rice vinegar and salt in bowl until smooth.
Step 3Cut off and discard root end (about 1/4 inch) of green onions and 2 to 3 inches coarse green tops. Thinly slice green onions. Cut tomato into about 6 slices and stack slices in 2 or 3 piles. Cut into bite-size pieces.
Step 4Combine onions, tomato and ground beef in medium mixing bowl. Add 1/2 of garlic mixture and mix thoroughly until well combined.
Step 5Cook ground beef mixture in skillet set over medium-high heat, stirring constantly until beef loses its redness and is lightly browned, about 3 to 5 minutes.
Step 6Place lettuce leaves on work surface. Spread 1 1/2 teaspoons remaining garlic mixture on each leaf. Place 3 or 4 tablespoons ground beef filling in center of each leaf and roll up. Serve 2 lettuce leaves to a plate, rolled side down.