Preheat oven to 350F. Lightly butter an 11x7 glass baking pan.
Arrange the chilies on the bottom of the casserole. Top with an even layer of the cheese and then the sliced tomatoes.
In a large bowl, whisk the eggs until they are frothy. Gradually whisk in the evaporated milk, flour and salt. Carefully pour over the layers in the dish. Bake 50-60 minutes, or until lightly browned. Serve in squares and garnish with sour cream and avocado slices.
Source: "Cooking with Regis and Kathie Lee", 1993