Bring water and 1 tsp vinegar to a light boil in a shallow pan. Make sure there is enough water to cover egg. While water is coming to a boil, slice bagel in half and toast. Place tomato, avocado, and cheese on top of toasted bagel. Poach eggs, crack into water and cook about 5 minutes, just until the white is set and the yolk has filmed over. Remove and place on top of bagel. Season with salt and pepper to taste. Serve open faced.