Boil the eggs – Cover eggs with cold water in a saucepan, bring to a boil, then simmer 7 minutes. Transfer to an ice-cold water bath for at least 5 minutes.

Peel and separate – Peel eggs, separate yolks from whites. Dice whites into small even pieces.

Strain the yogurt – Drain Greek yogurt in a fine mesh strainer or cheesecloth-lined colander for about 15 minutes.

Dice the cucumber – Dice 1/4 of a cucumber for the salad while yogurt strains.

Make the dressing – Combine strained yogurt, egg yolks, mustard, and lime juice; mash and mix until smooth.

Build the salad – Fold in diced egg whites, jalapeños, onion, cucumber, chili flakes, cilantro, salt, and pepper until evenly combined.

Prepare cucumber boats – Slice a whole cucumber lengthwise; scoop out seeds with a spoon or melon baller.

Fill and garnish – Spoon egg salad into cucumber boats. Top with black sesame seeds and extra cilantro. Serve immediately.