In 3-quart saucepan, heat oil over medium heat. Stir in onion, flour and salt. Cook 2 to 3 minutes, stirring constantly, until onion is soft.
In small bowl, stir soymilk and cornstarch with wire whisk until smooth. Gradually stir into onion mixture. Cook 5 to 6 minutes, stirring frequently, until thick and bubbly.
Stir in cheese. Cook about 3 minutes, stirring frequently, until cheese is melted. Stir in broccoli. Cook about 1 minute or until hot, stirring occasionally. Serve topped with popcorn.