Bring a large pot of water to a boil. Season the water liberally with salt (it should be very salty to taste).
Blanch the green beans for 4 to 5 minutes, stirring occasionally, or until they are crisp-tender and slightly squeaky between your teeth. It is important that the green beans be slightly undercooked as they will be transferred directly to the skillet and will continue cooking during this time.
Meanwhile in a large skillet, melt the butter over medium-low heat until lightly bubbling. Add the sliced almonds and sauté, stirring frequently, for 2 to 3 minutes or until they are starting to turn golden brown. Reduce the heat to low and add the shallots and garlic. Sauté for an additional 1 to 2 minutes, stirring frequently, until fragrant and lightly caramelised.
Using a large slotted spoon, transfer the blanched green beans from the boiling water directly to the skillet. Sauté briefly, gently tossing the green beans with the almond mixture until evenly combined and the green beans are tender. Add the lemon zest and lemon juice, toss once again, and season to taste with salt and freshly ground pepper.