Preheat the broiler (grill). Arrange the baguette slices on a broiler pan and top each slice with a sprinkling of basil, oregano and cheese. Place about 4 inches from the heat source and broil (grill) until the cheese is melted, 45 to 60 seconds. Watch carefully to prevent burning. Set aside.
Peel, seed and dice the tomatoes. In a large, heavy saucepan, heat the olive oil over medium heat. Add the onion and saute until soft and translucent, about 4 minutes. Add the tomatoes and tomato paste and bring to a boil. Reduce the heat to medium-low and simmer, uncovered, until the soup thickens, 20 to 25 minutes.
In a blender or food processor, puree the soup in batches until smooth and return to the pan. Stir in the milk, salt and pepper and reheat gently. Ladle into individual bowls, garnish each with 2 herb toasts and serve.