In a medium pot, over medium heat, add the canola oil. Stir in the onions and celery, and saute until the onions are soft and translucent, about 5 minutes. Add the garlic, red pepper flakes, and salt and pepper, to taste, and saute an additional 2 minutes. Stir in the crushed tomatoes and vegetable broth. Bring to a boil, then reduce the heat to a simmer. Cook, covered for 30 minutes. (Remove 2 cups of soup and reserve it for Round 2 Recipe Chicken Cacciatore.) Add the remaining soup to a blender and puree until smooth. Return the puree to the pot and season with salt and pepper, to taste. Serve hot with grilled cheese sandwich.
For Grilled Cheese Sandwich:
Heat a large grill pan over medium-high heat. Butter 1 side of each slice of bread. Lay half of the bread, butter side down, in the pan. Put a slice of American cheese on each piece of bread, then sprinkle 2 tablespoons of the Cheddar on top of each piece. Add another slice of American cheese on top of the Cheddar and finally cover with the remaining bread slices, butter side up. Grill until golden brown on both sides and the cheese is melted, about 3 minutes a side. Cut into triangles and serve with tomato soup.