Preheat the oven to 400 degrees F (200 degrees C).

Spread pecans evenly on a baking sheet. Toast in the preheated oven until lightly browned and fragrant, 8 to 10 minutes.

Whisk vinegar, Dijon mustard, sugar, salt, and pepper together in a small bowl until sugar and salt dissolve. Whisk in olive oil.

Toss salad greens, pecans, cranberries, onion, and feta together in a salad bowl. Drizzle with vinaigrette; toss gently to coat.