Whisk minced shallots, olive oil and lemon juice in medium bowl to blend. Season dressing to taste with salt and pepper.
Cut all peel and white pith from oranges. Using small sharp knife, cut between membranes to release segments. Combine arugula, fennel and onion in large bowl. Toss with enough dressing to coat. Add orange segments; toss to combine. Season salad to taste with salt and pepper and serve.