In 10-inch skillet, heat oil over medium-high heat. Add chicken and onion; cook 15 to 18 minutes, stirring onion frequently and turning chicken once, until onion is tender and juice of chicken is clear when center of thickest part is cut (170°F). Remove from heat; cover to keep warm.
Meanwhile, fill 2-quart saucepan 2/3 full of water. Heat to boiling. Stir in uncooked pasta (from Chicken Helper box). Gently boil uncovered about 15 minutes, stirring occasionally, until pasta is tender; drain. Set aside.
In same saucepan, mix hot water, half-and-half, tomatoes and sauce mix (from Chicken Helper box). Heat to boiling. Reduce heat; cover and simmer 10 minutes, stirring occasionally, until sauce is slightly thickened.
Cut chicken into slices. To serve, spoon cooked pasta onto serving plate. Arrange chicken slices and onion over pasta. Top with sauce mixture. Sprinkle with basil.