Boil the broccoli and red bell pepper in a pot of boiling water until fully cooked.

Remove the pot from the heat and cover it to keep the vegetables warm.

To prepare the sauce: Melt the butter in a non-stick pan over medium heat. Add the onion and garlic and sauté until they soften.

Add the cornstarch, mustard, and orange juice. Stir well until you get a thick sauce consistency.

Drain the broccoli and red pepper from the water and place them in a serving dish.

Pour the prepared sauce over them, toss gently to coat, and serve the broccoli salad immediately.