Preheat oven to 400ºF and grease an 8x8-inch baking dish with coconut oil or coat with cooking spray.
Whisk together the orange juice, rice vinegar, brown sugar, ketchup, soy sauce, garlic and ginger in a small bowl. Set aside.
In a large bowl, gently toss the tofu with the cornstarch, being careful not to break the tofu. Once the tofu is coated with the cornstarch, transfer it to the prepared baking dish. Add the bell peppers and pineapple, then pour in the sauce and gently stir to coat.
Place the baking dish in the oven and bake for about 40 minutes or until the sauce has thickened, stirring halfway through the cooking time. Let stand for 5 minutes, then serve over rice or quinoa and garnish with green onions.