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Heat a large cast-iron skillet over medium-high heat, then brush with the grapeseed oil. The oil should shimmer, but reduce the heat if it smokes.
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Arrange the shallots cut-side down in the skillet and let sear until deeply browned on both sides, 4 to 5 minutes. Transfer to a plate.
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Working in batches, add the beans to the skillet and cook, tossing occasionally, until crisp-tender and lightly charred in spots, about 8 minutes. Transfer to a large bowl and cover with foil to keep warm while cooking the next batch.
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Add the butter to the beans 1/2 tablespoon at a time, alternating with half of the lemon juice. Toss to incorporate.
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Add the shallots and half each of the lemon zest, almonds, mint, and parsley. Toss to mix and season with the salt and pepper.
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Transfer the beans to a serving platter. Sprinkle with the remaining lemon zest, almonds, mint, and parsley. Serve warm. Season with salt and pepper to taste.