Heat oven to 375 degrees F. Sauté onion in oil in skillet 3 minutes. Add chicken; sauté 5 minutes. Add seasoning and water; cook 2 minutes. Take off heat.
Spread 1/4 cup salsa over bottom of 13 x 9 x 2-inch baking dish.
Place 4 tortillas on microwave-safe plate; sprinkle with 1 tablespoon water. Cover with damp toweling; microwave on high 30 seconds.
Working quickly, brush one side of each tortilla with salsa. Place 1/3 cup chicken mixture in center of coated side of each; roll up; place, seam side down, in prepared dish. Repeat steps 3 and 4 with remaining tortillas, filling.
Mix half-and-half, remaining salsa. Pour over enchiladas; brush to cover completely. Sprinkle with cheese.
Bake in 375 degree F oven 15 minutes. Makes 8 enchiladas.