Spring Greens with Orange-Fennel Vinaigrette

2 tablespoons minced shallots

1 tablespoon fresh thyme leaves

2 teaspoons (packed) grated orange peel

1 teaspoon honey

1/2 cup extra-virgin olive oil

1/4 cup finely chopped fresh fennel bulb

2 tablespoons chopped fennel fronds

3 blood oranges or seedless oranges

12 cups torn assorted salad greens (such as arugula, watercress, mâche, and endive) or 1 1/2 five-ounce bags mixed baby greens

1 cup chopped green onions

2/3 cup walnuts, toasted