Add the cauliflower florets to a big bowl and gently rub in the olive oil using your hands. Sprinkle the cornstarch across and keep mixing until the cauliflower florets are nicely coated.
On a greased baking sheet, spread out the coated cauliflower evenly and bake for 15-20 minutes until the bottom slightly starts to brown. Afterwards, switch oven to grill and grill on high for 3-4 minutes just until tops start to brown. (Keep an eye on it to make sure the cauliflower doesn't burn!)
Meantime, boil the brown rice and prepare the sauce.
In a small saucepan combine coconut sugar, apple cider vinegar, 1/3 cup water, tamari sauce, garlic powder and ketchup and bring to a boil.
Dissolve the cornstarch in cold water and pour into the sauce, stir well.
Add the red bell pepper and boil until the sauce has thickened to your liking.
Serve with rice and garnish with thinly sliced spring onion.
The measurements for the sauce are just enough to cover the cauliflower but if you like a lot of sauce to go with your rice I would suggest doubling the sauce recipe.