Preheat the oven to 350°F and set the oven rack in the center. Lightly grease a 13 x 9-inch baking dish with cooking spray and set aside.
Add the tomatoes, seeded pepper, chopped onion, and bell peppers to a blender. Blend until completely smooth.
Heat the vegetable oil in a large pan over medium heat. Add the sliced onion and salt. Cook for about 2 to 3 minutes, until softened.
Stir in the bay leaves, curry powder, paprika, thyme, ginger, garlic powder, onion powder, and black pepper. Cook for about 1 minute to warm the spices. Add the tomato paste and stir for another 2 minutes.
Pour in the blended tomato mixture. Stir well and cook for 10 to 12 minutes, until the mixture reduces by about half and thickens.
Add 1 cup of stock or water and bring to a boil for 1 to 2 minutes.
Stir in the rinsed rice and butter. Taste and add more salt if needed.
Carefully transfer the mixture to the prepared baking dish. Cover tightly with foil and bake for 40 to 50 minutes, until the rice is tender. Check after 30 minutes and add more liquid if the rice looks dry. Fluff gently with a fork before serving.