Rinse Lentils: Rinse 1 cup of dried green lentils under cold water.
Cook Lentils: In a stock pot, combine lentils, 3 cups of water, and 1 bay leaf. Bring to a boil, then reduce heat and simmer for 15-20 minutes.
Drain and Cool Lentils: Once cooked, drain lentils and rinse under cold water to stop cooking.
Prepare Salad: In a bowl, combine lentils, 1/3 cup chopped red onion, 1/2 cup chopped red bell pepper, 1/2 cup chopped cucumber, and 2 tablespoons chopped parsley. Season with salt and pepper.
Make Dressing: In a separate bowl, whisk together 3 tablespoons olive oil, 1 tablespoon lemon juice, 1 clove grated garlic, 1 teaspoon dried oregano, salt, and pepper.
Combine Salad and Dressing: Pour dressing over the lentil salad and mix well.
Prepare Avocados: Cut avocados in half, remove pits, and scoop out some pulp to create space for the salad. Rub with lemon juice to prevent browning.
Stuff Avocados: Stuff each avocado half with the lentil salad mixture.