Steak and Tomato Salad

1/4 c red onion, finely chopped 1/4 c Tubby Olive Champagne Vinegar 1/3 c Tubby Olive Fern Leaf Dill Olive Oil 1 T Dijon mustard 1-1/2 lbs assorted colors of cherry tomatoes halved and medium heirloom tomatoes cut into large dice 1 lb grilled and chilled beef, sliced...