Trim outer layer of fennel bulbs; cut stalks from tops. Roughly chop enough green fronds for about 2 tablespoons; set aside. Using a mandoline or sharp knife, slice bulbs crosswise as thinly as possible. Discard tough core. Place sliced fennel bulbs and reserved chopped fronds in a salad bowl; add almonds.
Make dressing: In a small bowl, whisk together lemon juice, oil, and salt, and season with pepper. Pour dressing over fennel mixture; toss well to combine. Serve immediately.