ADD enough water to fill large skillet about 3/4 full. Bring to boil on medium-high heat. Meanwhile, mix meat, egg white, 1/2 cup each onions and basil, cracker crumbs and 2 Tbsp. cheese until well blended; shape into 42 (3/4-inch) balls.

PLACE half the meatballs in boiling water; cook 7 min. or until meatballs are done. Remove meatballs with slotted spoon; drain on paper towels. Repeat with remaining meatballs. Discard cooking water.

HEAT dressing in same skillet on medium heat. Add remaining onions; cook 3 min. or until crisp-tender, stirring occasionally. Add meatballs, tomatoes and remaining basil; stir to evenly coat meatballs. Bring to boil; simmer on medium-low heat 20 min. or until heated through, stirring occasionally. Meanwhile, cook spaghetti as directed on package, omitting salt.

DRAIN spaghetti; place in large bowl. Add meatballs and sauce; toss to coat. Sprinkle with remaining cheese.