Wash and trim broccoli and cauliflower; break into small florets. Put the broccoli and cauliflower in a serving bowl and add the red onions, bell pepper.
In another bowl, combine the mayonnaise, oil, vinegar, sugar, salt, and pepper. Add the dressing mixture to the vegetables and toss to blend. Chill thoroughly.
Garnish with cooked crumbled bacon just before serving.