Put the eggs in a small saucepan and cover with cold water. Place over medium heat and bring to a boil. Remove from the heat, cover and let sit in the water for 10 minutes. Rinse the eggs under cold water and let cool for 5 minutes. Peel and slice into rounds. Add the avocado to a bowl and mash well with a fork. Add the lemon juice and a sprinkle of salt and pepper. Divide the avocado between both pieces of bread and spread from corner to corner. Divide the hard-boiled egg between the toasts. Top each toast with a slice of tomato.