Heat oven to 350°F. Spray 2-quart casserole with cooking spray.
Meanwhile, in 10-inch nonstick skillet, melt butter over medium-high heat. Add onion; cook, stirring occasionally, until crisp-tender. Reduce heat to medium. Stir in 1/2 teaspoon salt, the cooking sauce and milk; heat to boiling. Stir in cooked rice and thawed broccoli until well mixed. Spoon into casserole.
Bake uncovered 30 to 35 minutes or until hot in center and bubbly around edges. Sprinkle with crackers.