Preheat oven to 350° F. Spread the pecans in a single layer on a dry baking sheet. Bake for 8-10 minutes, until they smell fragrant. Be careful not to toast them too long. Cool and roughly chop them on a cutting board.Place the sliced onions in a bowl and cover with cold water to mellow out the pungency. Let sit while you put the rest of the salad together.Whisk together the vinegar, oil, honey, mustard, salt and pepper for the balsamic vinaigrette. Set aside.Place the spinach in a great big serving bowl. Add the strawberries and drained red onions. Drizzle about half of the vinaigrette and toss to coat the leaves. Add Boursin cheese and pecans. Drizzle with a little more dressing and serve immediately. (Serve extra dressing on the side.)