Cook bean and rice mix according to package directions.
Meanwhile, combine salsa and tomato sauce and pour 1 cup of the mixture into a 9- by 13-inch casserole.
In a microwave oven on full power (100 percent), warm 2 or 3 tortillas at a time between paper towels, 20 to 30 seconds.
As tortillas are heated, spoon 1/4 cup bean mixture and 1 tablespoon cheese down center of each, roll to enclose, and place, seam down, in casserole.
Pour remaining salsa mixture over enchiladas and sprinkle with remaining cheese.
Bake in a 400° oven until enchiladas are hot in center, 20 to 25 minutes. Garnish the casserole with sour cream and olives.