Preheat oven to 400ºF. Place the radishes on a baking sheet and toss with vegetable oil. Salt and pepper to taste. Roast, turning half way through cooking, until softened and starting to brown (about 15 minutes). Reserve.
Bring a large pot of salted water to a boil. Cook the farfalle according to package directions. Drain and reserve.
Place the leeks in a saucepan, cover with water, and season with salt. Simmer until the leeks are soft (about 5 minutes). Drain liquid, reserving the leeks in the saucepan.
Add the radishes, farfalle, white beans, and pesto. Heat through and toss to combine. Adjust seasoning to taste with salt and pepper.