Bring a large pot of water to a rolling boil and salt it generously, about 1 tablespoon of salt per gallon. While it heats, fill a large bowl with cold water and a couple of handfuls of ice. You want this ready before the beans go in.

Add the trimmed green beans to the boiling water and cook for 3 to 4 minutes. You are looking for beans that are bright green and just tender when you bite through one, with a little resistance still in the center. They will finish in the skillet, so do not go past that point.

Drain the beans immediately and transfer them to the ice water. Let them sit for 2 minutes until fully cooled, then drain again and spread them on a clean kitchen towel or paper towels. Pat them as dry as you can. Wet beans will steam in the skillet instead of saute, and you lose the texture you just worked for.

Set a large skillet over medium heat with no oil. Add the sliced almonds and toast them, stirring frequently, for 2 to 3 minutes until they are golden and smell nutty. Watch them closely because they go from perfect to burnt in about 30 seconds. Tip them onto a plate and set aside.

Add the olive oil to the same skillet and raise the heat to medium-high. Once the oil shimmers, add the sliced garlic and cook for 60 to 90 seconds, stirring constantly, until it just turns golden at the edges. Do not walk away during this step.

Add the dried green beans to the skillet in one layer if possible. Toss them with the garlic and oil and let them cook, tossing every minute or so, for about 4 to 5 minutes until heated through and starting to pick up a little color at the edges.

Turn off the heat. Squeeze the lemon juice over the beans, add the lemon zest, salt, black pepper, and red pepper flakes if using. Toss everything together, then scatter the toasted almonds over the top. Transfer to a serving dish immediately and serve while hot.