Preheat the oven to 450 degrees F. Line a baking sheet with a silicone liner.
In a medium bowl, toss the cauliflower with 1 tbsp orange juice.
Place the cauliflower in a single layer on a baking sheet and bake for 15-20 minutes. Cauliflower should be just starting to brown on the edges.
While the cauliflower is roasting, whisk together the orange juice, soy sauce, maple syrup, and vinegar. Set aside.
Stir together the cornstarch and water until smooth and set aside.
Add 1/4 cup vegetable broth to a large pan over medium heat. Add the onion and garlic and sauté 5-6 minutes until soft.
Add another 2 tbsp vegetable broth to the pan and add the peppers. Saute 5-6 minutes until softened.
When the peppers are softened, add the orange sauce to the pan and turn up the heat to bring to a boil.
Once boiling, add the cornstarch/water mixture and stir well to incorporate. Simmer over medium heat until the sauce reduces and thickens to almost a syrup like consistency.
Add the cauliflower to the sauce when it's done roasting and stir to coat well.
Sprinkle sesame seeds over the top, if using, and serve immediately by itself or over rice.