Heat oil in medium pot over medium-high heat. Add onion, carrot, celery, and garlic. Saute until vegetables have softened, about 7-8 minutes. Add tomato - Italian seasoning, stirring to combine. Cover and bring to a boil. Reduce heat and simmer for 10 minutes. Remove from heat and blend soup until smooth. Season with salt and pepper. Return soup to pot and keep warm.
Heat nonstick pan over medium-low heat. Add ½ tablespoon butter and melt. Add both slices of white bread, allowing them to soak up the butter. Spread cheese on one side of the bread. Top with 3 slices of bacon per sandwich followed by more cheese. Stack the other slice of bread on top, buttered side facing up. Spread cheese on top of the bread and cook until golden brown on the bottom.
Melt the remaining butter in the pan. Flip the sandwich over and spread cheese on the top of the bread. Continue to cook for 3-4 minutes.
Flip sandwich over once more and let cheese on the outside caramelize and get crispy. Remove sandwich from the pan. Cut into bite size pieces. Ladle soup into bowls and top with grilled cheese and bacon croutons.