Meanwhile, in a large saute pan, toast the almonds over medium-high heat until golden brown and fragrant, 3 to 5 minutes. Remove from the pan, finely chop and set aside.
Blanch the string beans in salted boiling water until crisp but tender, 2 to 3 minutes. The salt will impart flavor as well as help keep the string beans crisp. Immediately drain and run cold water over the beans or plunge into an ice bath to cool and stop the cooking process, then remove and completely dry.
Return the saute pan to the burner over medium heat and melt the butter with the olive oil. Add the shallots, sprinkle with salt and pepper and cook until starting to brown, stirring occasionally, 3 to 5 minutes. Toss the drained beans with the shallots and add the lemon zest and juice. Cook to heat the beans completely through, 1 to 2 minutes.
Remove from the heat and season with additional salt and pepper if needed. Toss with the toasted chopped almonds and transfer to a serving dish.