Whisk together the oil, sugar, poppy seeds, mustard and vinegar. Refrigerate until chilled.
In a salad bowl, combine the mixed salad, mushrooms and dressing; toss to coat. Sprinkle with strawberries and pecans.
Try adding some crumbled gorgonzola to this salad for an extra special touch. You could also try substituting half of the mixed greens with a combination of cress and rocket; the peppery rocket is particularly nice in contrast to the sweet strawberries.