Method:
Preheat oven to 350°F. Toss onion with canola oil and a pinch of salt and pepper and place on a rimmed baking sheet. Roast until onion is soft and lightly browned, 15 to 20 minutes. Set aside to cool.
Toss lettuce, walnuts, tomatoes, berries and goat cheese in a large serving bowl.
For the vinaigrette, whisk together vinegar, lemon juice, sugar, salt and pepper. Drizzle in the oil while continuing to whisk, until vinaigrette slightly thickens. Taste and adjust seasoning. Drizzle dressing over salad, add red onion and toss to combine. Serve immediately