Hard-boil the eggs: Place the eggs in a single layer in a saucepan and cover with cold water by about an inch. Bring to a gentle boil, then cover, remove from heat, and let sit for 12 minutes. Drain and transfer eggs to a bowl of ice water for 5 minutes.

Peel and halve: Tap each egg gently, roll to crack the shell, and peel under running water. Slice eggs lengthwise and remove yolks into a medium bowl; set white halves aside.

Make the avocado-yolk filling: Mash the avocado with a fork until almost smooth. Add the cooked yolks, Greek yogurt or mayonnaise, Dijon mustard, lemon juice, cumin or smoked paprika, salt, and pepper. Stir until creamy but with a bit of texture.

Taste and adjust: Scoop a small bit onto a white to check seasoning. Adjust with more lemon, salt, or cayenne as needed.

Fill the egg whites: Using a teaspoon or a small piping bag, fill each egg white half with the avocado-yolk mixture.

Garnish and serve: Sprinkle with chopped chives, smoked paprika, or crispy bacon. Serve chilled or slightly cool.