Toast the raw oatmeal in a large heavy skillet over medium heat, stirring frequently, until it is browned but not burned (about 10 minutes). Set aside.
Melt the butter in a 4 quart saucepan, add the onions and sauté until softened, adding the garlic for the last two minutes. Add the chicken broth, tomatoes, and toasted oatmeal. Bring to a simmer and cook for about 10 minutes. Season to taste with salt and pepper.