Process lemon juice, egg substitute, and next 4 ingredients in a food processor or blender until smooth, stopping to scrape down sides. With processor running, pour vegetable oil through food chute in a slow, steady stream; process until smooth and thickened. Spoon over sliced tomatoes.
Kitchen Express: Stir together 1/2 cup mayonnaise, 1/4 cup chopped fresh basil, 2 tsp. coarse-grained mustard, and salt and pepper to taste. Serve mayonnaise mixture over tomatoes. Cover and chill up to 1 week.