Spread cauliflower, onions, and garlic onto a large baking sheet. Spray canola oil spray over cauliflower mixture.
Bake in the preheated oven until browned and tender, 30 to 45 minutes. Transfer cauliflower mixture to a 9x13-inch baking dish. Reduce oven temperature to 300 degrees F (150 degrees C).
Blend soy milk, tofu, vegan cheese, nutritional yeast, onion powder, lemon juice, basil, marjoram, oregano, parsley, garlic powder, and black pepper in a food processor or blender until sauce is creamy.
Pour sauce into a saucepan and cook over medium-low heat until warmed, about 5 minutes. Add kale to sauce and cook until kale is wilted, about 5 minutes. Pour sauce over cauliflower mixture and add tomatoes; mix well.
Bake in the oven until bubbling and lightly browned, about 40 minutes.
