Cook a couple of minutes. Make a well in the center of the mixture in the pot. Put the rice in the well and pat it down until it is wet. Cover and cook until rice is done, about 25 minutes. Add Tabasco sauce to taste.
Puree tomatoes in a food processor or food mill, then press through a sieve to remove seeds.
In a large mixing bowl, beat the pureed tomatoes, tomato paste, buttermilk and oil. Toss pureed avocado with 1 tablespoon lemon juice to hold the color. Season to taste with salt and pepper and a generous number of drops of hot pepper sauce. Refrigerate several hours before serving. At serving time, taste soup for seasonings.