To warm cast iron pan, add remaining 1 Tbsp grapeseed oil and let warm for 30 seconds. Add onions and sauté, stirring occasionally, until softened, about 4 minutes. Add garlic and bell pepper and continue to cook, stirring occasionally, until softened and starting to brown, about 10 minutes. Stir in cumin, coriander, and red pepper flakes, and let cook for 1 minute before adding canned tomatoes along with their juices, cilantro, and dill. Stir sauce together well and let come to a simmer. At this point, if you prefer a smoother sauce, use an immersion blender to purée sauce a bit. Nestle tofu into sauce and transfer pan to oven for 10 minutes.