Heat the oven to 425°F. Toss tomatoes, peppers, onion and garlic with oil, salt and pepper on two rimmed sheet pans and roast for 30 to 35 minutes until softened with browned edges.
Transfer roasted vegetables and their juices to a large pot. Add beans, broth and basil and simmer for 10 minutes.
Turn off the heat and blend with an immersion blender until smooth, keeping the blade submerged. Stir in balsamic vinegar.
Freeze after cooking: divide soup among 6 shallow freezer containers, refrigerate within 2 hours and chill completely. Leave 1 inch of headspace, seal, label and freeze for up to 3 months.
Reheat from frozen: loosen one portion from its container into a saucepan with 1 tablespoon water. Cover and warm over medium-low heat, stirring and breaking up the block as it softens, for about 15 to 20 minutes until the soup reaches 165°F.
Stir thoroughly before serving one container per portion, adding only a little more water if the soup is too thick.