Long beans are one and a half to three feet long and have a somewhat drier texture than string beans. Look for them in Asian produce markets, or try this dish with any fresh string or wax bean.
Heat oven to 350 degrees. Spread the walnuts on a baking pan. Toast until fragrant, 7 to 10 minutes. Transfer nuts to a plate to cool.
Bring a large saucepan of salted water to a boil. Add the long beans, and cook until they are just tender and bright green, 1 to 2 minutes. Drain the beans in a colander, and pat them dry with a clean towel. Transfer to a large bowl, and set aside.
Heat the olive oil in a medium skillet over medium-low heat. Add the walnuts, fennel seeds, and cumin seeds, and cook, stirring continuously, until fragrant, 1 to 2 minutes. Remove from heat, pour mixture over the reserved beans, and toss to combine. Season to taste with salt and pepper, and serve.