Combine chicken, 1 cup cheese, 1/4 cup Hellmann's® or Best Foods® Real Mayonnaise and onion in medium bowl; set aside.
Bring salsa to a simmer in large nonstick skillet over medium heat. Whisk in remaining 3/4 cup Mayonnaise and Bouillon. Remove from heat and keep warm.
Heat oil in another 10-inch nonstick skillet over medium heat and cook tortillas, one at a time, turning once, 1 minute or until heated through but not crisp. Drain on paper towels.
Spread 1/2 cup sauce in 13 x 9-inch baking dish. Dip tortillas in remaining sauce, then fill each with about 1/4 cup chicken mixture. Roll and place seam-side down in baking dish. Pour remaining sauce over enchiladas, then sprinkle with remaining 1/2 cup cheese.
Bake 20 minutes or until enchiladas are heated through and cheese is melted. Garnish, if desired, with additional chopped red onion.