Immerse each avocado half fully in fresh lemon juice to avoid browning (you can skip this step if preparing this dish right before serving).

Combine the mashed avocado with one teaspoon lemon juice, mayonnaise, and salt to taste, and set aside.

Discard the centers of the plum tomatoes and dice very finely.

Dice the shallot very finely and combine with the tomatoes in a bowl.

Add the apple cider vinegar, olive oil, and some kosher salt to taste. Mix well to coat.

Arrange a tablespoon of the tomato salad in the center of each avocado half.

Place a small mound of mashed avocado in the center of a plate (its main purpose is to prevent the avocado half from slipping).

Place a filled avocado half in the center of the mound and cover loosely with two slices of lox. You can place small pieces of lox at the base of the avocado as well, and garnish with chopped herbs. Drizzle over some more olive oil to finish.