This is how to make my tomato and mozzarella with olive oil and herbs salad with 1-up mushrooms. I made these for a Changeling: The Lost character creation session, and they were a big hit!
Step one: Use Campari tomatoes — they are bigger than cherry tomatoes, and rounder than plum tomatoes. I just washed them and cut off the part with the stem.
Step two: For the mushroom stem, I used string cheese, the mozzarella type, and marinated it in olive oil, italian spices and garlic overnight. It didn't really soak up any of it so you could probably get away with giving the cheese a quick dip. I used 1 inch (rough) pieces.
Step three: Put the cheese and tomato on a toothpick. If I had to do it again, I would probably use skewers, cut to size, because the toothpicks weren't quite long enough to put in the lettuce without messing up the "paint job."
Step four: Painting on little white dots of cheese with a toothpick. I used whipped cream cheese but you could probably use sour cream or ricotta cheese.