Bring a large pot of salted water to a boil over high heat. Fill a large bowl with ice water. If using fresh English peas, add to the boiling water and cook until tender, about 1 minute. Add the snap peas and cook until bright green, about 2 minutes, then add the snow peas and cook 30 seconds. Drain the peas and plunge into the ice water to cool.
Heat the olive oil in a large skillet over medium-high heat. Add the shallot and cook until soft, about 2 minutes. Add the walnuts, dates and cayenne and cook until the nuts are slightly toasted, about 1 more minute.
Drain the peas, shaking off the excess water, then add to the skillet (if using frozen peas, add them here). Add 1 teaspoon salt and cook, stirring, until heated through, 3 to 5 minutes. Add the walnut oil and toss. Add more salt to taste.