Flaky Mushroom And Gruyère Tarts

Name: Flaky Mushroom And Gruyère Tarts
Ingredients: 1 sheet puff pastry (half a 17.3-ounce package), thawed; 4 tablespoons olive oil; 10 ounces assorted mushrooms (such as button, cremini, shiitake, and oyster), sliced; 1 shallot, sliced; kosher salt and black pepper; 1/4 cup dry white wine; 4 ounces Gruyère or sharp white Cheddar, grated (1 cup); 1 teaspoon Dijon mustard; 1 teaspoon white wine vinegar; 4 ounces mixed greens (6 cups); 2 radishes, thinly sliced; 1 tablespoon chopped fresh chives